That's a Mountainsmith Lookout 45. Lots of features. Here's a mini-review:
-Hydration bladder pocket
-water bottle pockets that take 1L Nalgenes
-stretch pocket on the back with compression strap for main bag
-big pocket on the removable lid, valuables pocket under the lid, tabs for mounting items to top of the lid
-tool loops on the lower outside of the bag
-reinforced D loops for hanging gear on the upper outside of the bag
-extendable compression straps for items outside the bag on the sides or back, that will also compress the main bag down to *nothing*
-sleeping bag compartment with a divider held by small fastex buckles so that it can be separate from, or part of, the main bag. Also has compression straps to compact the load, or haul items on the outside.
-load lifters up top, and stabilizer straps at the bottom to the waistbelt
Only real downsides are that the torso length adjustment straps can slip and have to be tied off under the padding where they adjust, and the padding itself isn't breathable, so you get a sweaty back, even in mild temperatures. I had it up for sale, but am glad noone bought it, since I decided to start using it again. From now 'til fall I'll be sweating all over when hiking anyway, so having a "sweatier" back really doesn't make much difference.