This is a hydration pack with bells and whistles. There should be a better set of instructions to get you up to speed on the design, so you can better use the features.
You'll need to take a trip or two out with it before you begin to understand the value propositions. I realized after the third hike with it that I'd never thought about the backpack yet it was handy, my back wasnt sweaty from it sitting on me, and everything was placed as it should be. If it works, you shouldn't have to think about it, right?
So first, sizing - I'm 6'4", 205lbs, with a 36 waist. I bought the M/L and first thought (as the previous reviewer seems to) that the waist wouldn't cinch down far enough. It fit me very well once I got the idea of how the straps allow you to make multiple adjustments. I agree that it can leave you with extra strap if you cinch down super tight, but that didn't cause me any grief, plus nothing a rubber band doesn't fix I'd guess.
Second - capacity. For hiking I carried two sandwiches, a king can beer, two small bags of chips and had 3 liters of water with me. Then stuffed a jacket in the back outside pocket. Worked great. For biking I put in 2 tubes, a hand pump, tire levers, and a patch kit and could fit a sandwich plus a beer bottle (critical, right?) without crushing my grub. Again, room for jacket outside. Never have used the side pockets, so can't speak to those.
It's NOT a full backpack, but is designed to be a medium-sized multitool pack, between the ultralight Raptor 6 and a normal backpack.
Only complaints thus far are drying out the bladder (havent found an optimal method yet), and when you're full up on water and lean over, putting pressure on the bladder, water can shoot out of the mouthpiece.
Makes for a nice clown's flower...