This backpack is one of the most comfortable packs that I've ever used. Its weight to volume ratio is great: 3 pounds for 50 litres (its pretty hard to beat that). The only concern I had with buying this pack initially was the fact it was so light I thought it might not be durable enough (don't worry, its very durable). This pack has held up great to all sorts of trouble that I've put it through.
The only grip I have about it is the way the frame is built to create the ventilation chamber. It makes retrieving bulky things from the bottom of the pack difficult. It also makes carrying things like bear cans nearly impossible. Note: these grips wouldn't stop me from buying this pack again but this is the reason it didn't get a 5 star rating.
The things I like: The hip belt pockets are great to keep snacks, maps and other little things necessary for quick access. The hip belt itself is very comfortable and distributes the pack weight evenly. This thing weighs simply nothing by itself (love that). The ventilation chamber is great for hot days (and can be packed with gear). There is also a cool pouch for a hydration bladder and two outside pockets for water bottles (nalgenes fit great in these).
All in all this is a great backpack. I've had my pack seriously overloaded with winter gear and it still handled the load great!