feels like a hug!
I looooove this pack, and have recommended it to many trail running friends. The fit is so incredibly comfortable and snug that it really does feel like it's hugging you, and when I run with it I forget it's there (always a good thing!). It doesn't bounce, move, chafe, or any of the other bad things my old pack did.
Another selling point for me (which few of the other brands have) is the front pockets. There's nothing worse than having to take off your pack at 40k just to get more gels out... with this, I can fit lots of gels in the front. Also super easy to fill without taking the bladder out.
Someone below mentioned that the bladder sags as it empties--I avoid this with a couple of safety pins at the top to keep it standing.
While I love the wide opening of the bladder for easy refill, the bladder is quite hard to dry out because it collapses on itself. Also, I find the mouthpiece really difficult to open and close, especially if it's cold out and my fingers aren't as nimble as usual. Aside from those minor issues, this pack is by far my favourite and worth every penny!