Overall, this is a great backpack - it's functional, it holds a lot of stuff, and the fit is very comfortable. (I'm 5'6", and the small fits just right, and the harness is the right size, compared to other brands.) I'm a Gregory fan.

Where do I start?

First off, big kudos to these guys for having such amazing customer service and helpful employees. Our packs were lost in transit by UPS. Zach managed to find me a replacement pack, along with a pack for my gf, and got it to me overnight. What could have been a terribly disappointing set back, turned out to be no problem at all!

Bought this pack to replace a Northface pack I had for several years. It's first trip was to the Sabine National Forest and the Indian Mounds Wilderness. During our week trip I put this pack through serious hell. It was ziplined through the trees, hauled through the mud, dropped, slept on, stuffed to excruciating levels, and hauled up the side of white cliffs. This pack is very versatile. It rained the first few days we were out, and all my gear stayed perfectly dry.
A few things worth noting;

Zippers are rugged and do not leak.

A lot can be strapped to the outside of this pack, and I do mean a lot.

The bags compression ratio when not full is amazing, and can and has been used for day excursions.

The bladder sack is huge, but is on the outer most point of the pack, store your water bladder in a box or cooler or stiff container during transit nozzle up. When in use, place a 10x14 piece of cardboard between the material of your pack and your bladder to help protect the bladder from thorn, nail, branch, etc, punctures. This also adds a little durability to the backside of the pack in case you find it necessary to bail on your pack while being chased by bees. (amazing how fast you can move through the forest when being pursued by bees isn't it?)

The waist belt is awesome with lots of storage.

The bright color keeps it highly visible even in foggy conditions.

The suspension of the pack is fantastic, even with about 50-60lbs of gear loaded down on the pack, the load remained balanced and easily managed.

The one thing I have against this pack is I ran out of pockets! I'm a little OCD about having things stored properly, so I'll be investing in some stuff sacks to better separate the goods. Over-all I'm loving this pack!

Another bit of advice, practice disassembly and reassembly of the pack before your first trip with it. The amount of buckles and loops all being very close together can be somewhat confusing, and in my gf's case, very irritating.

Great buy! especially for the price!

This is a Great pack. I didn't know that Gregory made such a sick pack- but now I do. It is super light. The ventilation next to your back is great- it sort of archs away from your back and it is so nice and breezy that my camping friends often thrust their arm through this "breeze-way" when I first put it on because they are so amazed.

This is a great pack. I was previously using an Osprey Kestrel series which wasnt great for more than an overnighter but if you had too much weight it in it was a bear. Either way, I packed the Z55 up a couple weeks ago with about 30lbs of stuff for a weekend and put together a nice 25 mile hike. This pack acted like it didnt exist on my back. It held everything with room to spare (more stuff than I realistically needed). This will be my go to pack for everything now. From ultralight overnighters to big weeks. I think this thing could handle it all.

Also on my weekend venture I did some serious bushwacking and the pack did not get a nick or scrape what so ever!

All around buy this pack.

...like a thanksgiving turkey, she can handle it. i loaded this thing up with way more than i originally thought i would need. maybe i overpacked for a four day trek through the everglades but it was well worth it. and keeps your back very cool. you can strap a whole lot more to the outside of the pack than it may seem in the photo.

The Gregory Z series packs are my favorites, and not just me, I have seen many through hikers wear this on the AT. This pack is so comfertable, and has a great design. The arched back gives you great ventilation to keep you cool. Then there is the bucket pocket. I keep my camp shoes and all my rain gear in there, and there is room for more. It is perfect for large bulky items, anything you need to get to quick, or even wet or realy dirty items you don't want iside your pack. The zippered front pocket is large and more usefull than I first thought. I also appreciate the side access to the main compartment. The only thing to consider is if you carry a heavy pack, over 35 pounds, try a different pack.

I love this pack anyway (Great design and suspension, well thought out, light and capacious and a great deal, relative to Osprey and Arcteryx) but I have to give it extra kudos for putting up with a 3.5 hours hike in pouring rain this weekend with no cover. It did a pretty good imitation of of being waterproof. The only thing wet in the main compartment of my pack was the insulated synthetic jacket, which was up against the fabric on the base, which seems to be a lot less water resistant than the fabric the rest of the pack is cut from. So, on top of the fact that this is my favorite pack in the world at the moment, it just added "almost-waterproof" to the pro side of things. Well worth checking out if you are looking for an overnight or light weekend pack, especially if you are thinking about the Osprey Atmos/Stratos duo. Two thumbs up, Gregory.

I've had this pack for a while now and mainly use it for overnight to 3 day trips. I find it carries weight very well and i get a good amount of ventilation on my back due to mesh back panel. I'll post a pic soon to show the open area between the mesh and backpack frame. The pockets on the hipbelt are great for storing small items you need close at hand. I use them for my camera and compact gorillapod tripod which i also love. The shoulder straps have areas to clip small items onto, i usually clip on my knife. I also find that the strap setup for securing trekking poles to the back of the pack works well. I do have two gripes with the pack design though. One, there are no easy access pockets for water bottles. I don't know about everyone else but i don't like using hydration bladders when backpacking because i drink alot of water and don’t like having to pull stuff out of the pack just to get the full bladder back into the sleeve every time i refill it. I like my nalgene so i just purchased a fabric bottle holder and attach it to the strap that connects the hipbelt to the bottom of the pack. Works great and keeps my bottle close at hand. Second, the straps on the bottom of the pack don’t have buckles, they just have slide adjusters for the webbing. I like attaching my pad to the outside of the pack and getting my z-lite in those straps was hard when the pack was full, even when the straps were fully lengthened. I solved the problem by just cutting the straps, removing the sliders, and attaching some plastic buckles to the ends. Now i just buckle the pad on. Overall a very good pack.

Great pack all around. My first trip with it was to steal apples from a tree in Logan, UT. It carried 35+ pounds of apples so well I couldn't even feel the weight of guilt on my conscience. Next trip was a 20 mile overnighter. Room for everything you need for shoulder-season camping. Hip pockets are great--perfect size for a digital camera and Leatherman. My one complaint is the pack doesn't have water bottle side pockets so for those of us still living in the pre-bladder world it's a pain to pull out bottles from the main compartment when you're walking. Great pack.

Packs need to be tried, since no one pack is right for every person. That said, my Z pack the best pack I've ever used. I used it to hike the JMT last summer with 38 pounds on re-supply day. I used it this winter for a six week expedition in Chile and Argentina. It held all my gear for the entire trip!
I've attached a stuff sack/bottle carrier on the belt, since I prefer not to use the bladder option. The front belt pockets hold my camera and glasses.
When there is bulky stuff to carry the huge back pocket expands. The pack is so adjustable, I use it as a daypack by tightening all the adjusting pulls. It is a good idea to familiarize yourself with all the straps before you set out.
It is very sturdy and has held up well under rough conditions. Pretty water tight in the few light rain situations I found myself.
It's a little heaver than my two ultralight packs, but OH so much more comfortable!

I used this pack to hike in for a basecamp type trip. 8 miles in and with about 50 pounds (7 days). It was overloaded but showed no signs of wear. Created a hotspot on my lower back. But that was probably bc it was overloaded (or my pants). The hike out with less food was perfect. I liked it so much, I bought the womens version for my wife. We both wore them into the grand canyon, down to the river and back out. They were great. The pack sits away from your back in the middle, and allows for fantastic cooling. It was definitely appreciated in the canyon. It is cooler than wearing a camelback.

I use the Z55 as my primary pack. I purchased it one year ago after it was picked by National Geographic for the gear of the Year 2008. I have taken this pack on week long adventures and it distributes the weight like a dream. Honestly like a dream! Over the last year I have been switching out much of my light gear to accommodate even lighter gear.For example My new tent weighs 13oz plus stakes and using trekking poles (tyvek floor)(old tent was 39oz), My pad is the small aircore (16oz) (and yes I am aware of the neoair - I'm just not very fond of it), my pot is a titan kettle (used to be GSI soloist). I use the MSR miniworks filter (I know heavy at 15oz - I'll explain later), my sleeping bag is a Montbell UL down hugger #2 (for me the perfect all around 3 season compromise) My base weight three season is now a respectable 6-7lbs(not including my pack which I will get to). The real weight comes in when I need to carry food for a week w/out resupply (plus 1 - 3 liters of water). figure depending on the cuisine about 1.5 - 2lbs a day if I am treating myself really well - and why not I deserve it. Bare with me there is a point to all this - Im going get to the point of this review shortly. People have different reasons for hiking and many chose to hike light and honestly I began my hiking foray within the last two years looking to hike light from the onset. Some people have weak knees, others are survivalists, others race trails and each oz costs them time, while some just enjoy seeing to what extreme they can push themselves (regarding clothing, shelter and food). My reason is pure and simple I am lazy, I have no desire to spend a week in Yellowstone, the Appalachian trail, Rocky Mountain National Park or wherever hauling 40 - 60lbs like some sort of human donkey. frankly if that was the only way to hike Id rather stay in bed, watch TV and eat bonbons. Plus being a former NYC urban rollerblader traveling for me means being swift, and nimble - jumping curbs, and weaving through midtown traffic, and grabbing NYC transit bus rear wheel wells so I dont have to blade uphill to get to the MOMA or class. My approach to hiking is the same I want to be able jump a stream, stomp through shrubs, slide down a steep hill rather than take the long way or even bend down and smell a flower with my pack on. I dont want to be separated from nature because I am carrying crap I dont need like three pairs of pants, two fleece and a frying pan. I WILL BE WEARING THE SAME SMELLY CRAP I STARTED MY HIKE IN TWO WEEKS AGO - AND ILL LOVE EVERY SECOND OF IT - if i need to I will find a stream and break out the bronners and scrub my one pair of pants in my boxers (two pair if you must know) like they did in the old west. Don't get me wrong I enjoy comfort as well which is why I carry the air core since it allows this side sleeper to sleep like a baby, and the filter because I want my water to BE CLEAN, taste clean, and smell clean. Chemicals, and 3oz UV pens may kill god knows what creatures eggs are in the water but the dead eggs are still in the water - plus what sane person chooses to drink water with bleach in it - not I.
Now to the Z55 after reducing my weight this winter I figured perhaps it's time for a new pack. So I ordered the touted Osprey EXOS 46. It came in the mail I loaded it up 25lbs and the straps cut into my shoulders (and trust I adjusted the straps every which way for 45 min. I wanted the pack to work)I even ordered the larger size to see if it was a fit issue (it wasn't). much of the weight was not placed on my hips with the exos - it was on my shoulders further the pack wobbled and bobbled on my back when I tested it on steep stairs (then again packs are like shoes and the Exos was not the pair for me). No way am I reducing weight just to suffer that completely defeats the purpose - hiking is not about pain for me it's about pleasure. So instead I removed the lid on my Z55, and cut the remaining excess straps (and there are a lot). This pack hugs my body, my back breaths, and the waist straps are a dream. It carries everything flawlessly, I am now considering the Z35 for a pack with less volume (and yes pack suggestions are welcome if you understand my hiking philosophy) only those that own this pack will truly understand how sweet it is and where I came coming from, and until the day comes that a lighter pack provides me the same comfort while strapped to my back for 10 - 12 hours while I hike for multiple days - I will stay devoted to the Z55. - so if you are considering it go for it. There is one annoying issue I have with it - theres no bottle mesh, they expect that everyone wishes to soley rely on a platy. I would like a water bottle mesh pocket. This pack is great overall and you can take that to the bank. Shoot I got a math test in 5 hours!

I really liked this pack, unfortunately I had to send it back because I needed a little more room than I thought, would have gone with the z-65 if backcountry had it.

I like how this pack is lightweight, but extremely comfortable. I felt as if everything was close to me and my balance wasn't thrown off because I had a bulging bag on my back. There was plenty of space for most of my stuff and 30 pounds felt feathery. The waist belt is very comfortable and easy to adjust, and the pockets on the belt come in handy.

The only issues I had were:
There wasn't a side pocket for a water bottle. In order to store stuff with somewhat easy access, you would have to put it in the front pouch but this would still require you to take off the pack in order to gain access to it. The only other problem was the amount of straps. While it was nice that you were able to adjust basically everything, it was kind of annoying to have 10 straps hanging down.

Well, it's going with me on the PCT in 2009. As of right now, it's the most comfortable pack that I have owned. The shoulder straps are soft and supportive right from the get go and the waist belt, with pockets, is very comfy. I like that the hood pocket is not as large as other Gregory's (don't like to put alot on top). I'm so far able to stuff all that I need to backpack with some room leftover. I will let you know what I think of this after the trail.

I haven't logged too many miles with this guy yet, but so far it's more than what I expected. When looking for a new pack I did a lot of research and tried on several packs. I can't believe how well the ventilation and padding worked. I'm usually somewhat sore after a backpacking trip, but my shoulders felt nothing after my most recent trip. It handled very well in some rough terrain and all of my gear stayed in place. You can pack this backpack very well too. It has several straps to tighten it down similar to a stuff sack. I think this is really helpful for the weight distribution. Bottom line is that it's loaded with a lot of features and for light backpacking, I doubt you'll find a better pack.

bad things: (1)the zipper pulls fell off. no big deal: replaced with string.(2)no water bottle holders! weird. no big deal. bought a camelback. much better.(3)butt slid in winter. scratched up the bottom. solution: cover with duct tape when you plan on beating it up.
awesome pack. great dorsal ventilation. comfortable + light. good for a day hike, better for an UL overnight/multinight trip.pockets in hipbelt great for a small(one clif bar per pocket)snack or a camera. bottom line: great pack that'll get lots of use.

I had the G35 and decided to buy this pack when it came on sale since I could use the extra room for hiking the Colorado Trail this summer and the mesh panel for ventilation is much cooler. I've taken it on a couple of 3 day trial trips and it's been great. I'm normally with my wife, so one of us carries a water bottle on the outside mesh pockets (which the other person can grab) I stick my water bladder in the outside bucket pocket since it's easy to access. You can definitely go lighter on packs, but it shelters the load really well and is very comfortable. Last weekend I carried an extra 4 liters of water we needed for a dry campsite up a couple thousand feet with no problem.

I've had this pack for two trips now and have absolutely loved it. Packed to the gills, it still felt great on my back. I could wear this pack all day and not have a complaint.