Others have done a great job describing this nice pack. This comment is about sizing.
I'm 5'11", 165lbs, and usually wear a waist size of 33. Reading the measurement specs I figured I could either go with a large or medium Nitro. Turns out I was right, but for me the medium was a much better fit.
I originally ordered a large based on experience with other brands and the slightly larger capacity. The frame was on the long side for my back, but the real deal-killer was the large size of the waist belt. Had to cinch it and the shoulder straps way down. If I were mostly using the pack for winter I might have kept it, but that's not my plan.
I decided to swap the large pack out for a medium and am very happy I did. Thanks to Backcountry for the easy exchange.