I tried one a ton of packs before settling on this one. No other pack even came into the ball park of comfort this thing has (for me). The rotational hip belt is just awesome (also, the padding on the hipbelt is next to none). The adjustable suspension is very easy to adjust. (both height and width).
This pack also has enough compartments to conveniently organize without getting out of control. Arc'teryx has accomplished this with much style; this pack does not look too "busy". (in my opinion) The U-shape access is truly one of it's key features. I usually just go to this to get anything out of my pack. You can set the zippers in different locations so you can have direct access from the either side of the pack, not just at the very bottom. This is convenient if you have a sleeping pad or something else strapped to the bottom, or something strapped to the compression straps blocking one side.
As others have stated, this pack has a small water reservoir. Awesome pack, top quality, don't hesitate to purchase.