Unbelievable pack! I bought this pack after testing out many comparably sized packs, and by far, this was the most comfortable. The interchangeable hipbelt is great. I've got a fairly small waist for my height, and many of the "Medium sized" packs I tried were too large for the waist. Because you can buy a Medium pack, and swap out the hipbelt, you can truly customize the pack's fit to your body.
On the trail, the pack swallowed the weight and the compression straps kept things from shifting around. The pack has a removable sleeve for the internal bladder, and straps to convert it to a (very) small backpack for day hikes. It's a great pack, very durable and well worth the money. If you want the hipbelt custom molded, make sure you have an authorized Osprey dealer close by to do it.