It doesn't have all that much room, so you have to be careful in how you
pack, but if you can fit all your gear in here, it's a great choice.
Good: Very very comfortable. Reverse-pull hip buckle. You can fit a 2L water bladder in the empty space between the frame and the mesh back
panel. Plenty of straps to hold a sleeping pad, ice axe..., and places
to attach extra straps for attaching even more. Nifty drawstring closure
that's easy to open and tighten. One main compartment, two tall outer
compartments, and a lid, for keeping stuff organized. Two hip-belt
compartments for quick-access items. Elastic loops on the shoulder
straps for keeping a tube in place.
Bad: The hip belt isn't very beefy. The lots-of-compartments thing may annoy some. It may be difficult or impossible to fit a bear canister (haven't tried yet).

Got my Osprey Atmos 50 and I love it. This pack fits everything I need for a few days out in the mountains. Plenty of room inside and the outer pockets are easily accessible for smaller items and things you'll need more frequently. This is a very comfortable pack, adjusts very well for fit and the compression straps snug down all of your gear nicely. You can also have your water tube come out of either side of the pack. I highly recommend this pack for anyone going out in the wild for a few days.

After hiking over 3,000 miles this year with the Atmos 50, I can attest to the quality and durability of the product. Like all Osprey packs, it takes a day or two to break in the shoulder straps, and then you’re good for a decade. I think it’s funny how outdoor gear sales people try to convince would-be customers that packs like this can’t handle the needs of extensive trips. Well, leave the canned food and the blue jeans at home, and you’ll be fine. I love this pack. You get the best of the internal pack with the breathability of an external frame. If I could have any pack in the world, for long-distance hiking, it would be the Atmos 50 I already have. Sure it’s dirty and has a few small dental floss and duct tape patches, but the pack has no major issues and has treated me well.