Exos vs. Atmos...Exos wins
I am a longtime Atmos 65 user and was hesitant to get the Exos, worrying that the bag didn't have enough meat on its bones to last in the backcountry. After using it this weekend, I am moving exclusively to the Exos. While reviewing the Exos here, I will also try to compare it to the Atmos. I try to shave weight where I can, which was on of the reasons I gave the Exos a go.
Weight/sizing: I have a 19in Torso so a medium Osprey pack fits me well. The Med Atmos weighs 3lbs 9 oz, while the Med Exos is 2lbs 9oz, so there's a pound saved right there. I would note that like the Atmos, the should strap suspension (i.e. the torso lenth) is not adjustable, as it is on the Talon series.
Straps/buckles/zippers: much smaller/thinner on the Exos, which is how Osprey was able to save weight. The zipper pulls are smaller, the straps are notably thinner (especially the side compression straps). Having said that, the straps appear to be just as durable as the thicker Atmos straps and I did not have an issue at all. I was shocklingly surprised how comfortable the shoulder straps were, too. While they have a little less padding than the Atmos, there was no sacrifice in comfort. Wait belt looks slighlty different but is very similar to the Atmos (with the exception of a thinner waist strap).
Interior space: The Exos does not have a sleeping bag pocket (another way to save weight), so your bag goes right inside. Basic math says the Exos 58 should be 7 liters smaller than the Atmos 65, but in all honesty unless you are packed to the brim, there is plenty of space in the Exos. Here's what fits inside: Atom 40 degree sleeping bag, Neoair pad, Fly Creek UL2 tent (with the poles, all inside the pack), Snowpeak 1400 cookset (w/ gas and stove nested inside), my "emergency" stuff sack with meds etc, extra fleece, rain gear, 2 days food and a nalgene. With all this, there was still PLENTY of room to spare. I would estimate that I had the pack 70% full. If you were going winter camping and/or needed a bear canister or something, this pack would be fine.
Other features: like other reviews said, it would be nice if the gear straps on the bottom clipped on an off. I tested it and the Fly Creek fits in the allotted space with ease, as most smaller tents would I would think. Water storage is typical to other Osprey packs, as is the stretch pocket on the front. There are 2 front zip pockets which are nice for easy access.
All in all, the Exos is a stripped down version of the Atmos, but I'm glad I switched. The bag is durable, light, of Osprey quality, and while its appearance may be a bit misleading, this bag is tougher than it appears.