I followed Salomon's sizing chart and ordered an M/L, and before running with it I thought it would be too small. This morning I took it on its maiden voyage though, a 7 miler with 1600ft gain, and I can comfortably say that the sizing is correct.
The fit of this pack is really nice: It moves with you. If you order it and you think it's too small, I recommend taking it out for a spin before deciding to exchange for a larger size. Trust Salomon's engineering, or, at least give it a shot.
The back pockets are nice and big, but I had a hard time reaching a loose gel and bar I had stuck in them. I'll probably plan to not keep any back there and only stick things in the back that are bulkier to make reaching them easier: a hat, jacket, gloves, headlamp, or maybe a ziplock bag full of snacks.
The zipper pockets are great, three in total. I put my keys in the zippered pocket on one side and my wallet on the other and I could not feel them as I ran. The small pouches in the front above the water bottles are great for small bars, GUs, and salt capsules.
Soft water bottles are a great addition in this model over hard bottles with over vests, which tend to bruise your chest after long runs. I found that the water bottles begin to flop around a little once you've sipped from them--fun fact, you can sip from them without removing them from their pockets! One recommendation is that once the bottle is empty, take a second and blow it full of air to inflate it and then stick it back in its pocket; this will prevent it from flopping around or falling out of the pocket if you bend over to tie your shoe or pick up an arrowhead.
Since I was out solo in the backcountry, I appreciated the pack's integrated whistle, should I have needed to yell for help, the whistle would've made it much easier to guide people to my location. --On this note, there's also the safety blanket included, which is another reassurance to tuck into the back of your mind as you go out seeking adventure.