I don't have much to compare it to, but I love this pack and wouldn't change anything about it. I have used it 6 or 7 times now and I have zero complaints. The horizontal lumbar bladder is awesome. I never feel my water sloshing around or feel the weight of the water since it rests right on the hips. You don't have to take the bladder out of the pack to fill it up, but it does go in and come out really quickly, unlike some of the other lumbar packs I looked at. There is ample room for tools, tubes, food and extra layers, but it looks and feels very small on your back. The most exterior pocket which is just closed with a clip is nice for stuffing a layer that won't fit in the main compartment into. The waist strap pockets are great for carrying a phone/camera and food.
For girls, I think the fit is great. The straps are adjustable to probably most body types and chest sizes. I am 5'9", average size and it fits well with room for adjusting.
I never even notice it's on while I am riding, and that's probably the best part!