I used this backpack out for the first time in mid-May while on a three-day ski trip to Snowking Mountain in the North Cascades. I was very surprised at how much it actually holds, internally and externally. We brought skis and carried them and our boots on a climbing trail for about 3 miles and 2,000 vertical feet. No issues here.
I am not a fan of a bunch of external compartments and internal dividers. I generally don't buy backpacks like this. That being said, it worked well with this pack. I especially like the design of the pack lid. Separated into two compartments (which seemed weird at first), the bladder compartment fit my 2 liter camel back and the other compartment served well for map, sunscreen, headlamp, snacks etc. The bottom sleeping bag compartment was also nice. No need for a stuff sack as it fit perfectly down there. Side zip to the main compartment was also super helpful.
The lid detaches and the shoulder straps of the main pack come off to make an awesome and comfortable day pack. Unlike the larger pack however, it does not have any external straps or ice axe loops. This is a major shortcoming for the system. I did not use it for the summit push as it was unable to accommodate some necessary equipment. I instead had to use the larger backpack itself, which synches down to a fairly decent size. My crew and I were camping in a floor-less, Black Diamond Mega Light 4-Person Shelter in the snow. Leaving gear behind in this lightweight and only semi-protected system was not ideal as I emptied the backpack for the summit day.
The 400D nylon with teflon coating was un-phased by the North Cascades brush on the approach and snow and ice on the mountain. Should note that the material is tough as hell but not waterproof. I left it sitting upright on the snow as we assembled camp for maybe an hour. My sleeping bag was in the bottom compartment and was actually a bit wet when I pulled it out. Not a big deal for this trip, but on something extended may prove to be a problem. If I went out again and expected rain in the forecast or to camp in the snow I'd line it with a garbage bag.
Overall a comfortable, light, tough, well-designed backpack for the right trip. I look forward to taking it later in the summer for some flat backpacking trips. Despite the surprising comfort and ability to carry skis, shovel, probe and an ice axe, I won't be climbing more mountains with it as it is not as waterproof as I want nor is the daypack compatible for ice axe, picket or other technical gear (the daypack is awesome though, and would be great for non-technical trips).
It takes a lot for me to rate a backpack at 5 or even 4 stars. I expect my rating to change later in the summer as I use the pack for a different type of trip.