I have both an Osprey Stratos 40 and a Stratos 24 that I like. They are descendents of the Atmos line, but not as advanced or light as the new Exos. Main selling feature for me was the air mesh back panel. Not that you will feel a breeze back there or anything, but it is much cooler than padding against your back. The reduced volume between mesh and pack will be beneficial. I think the Exos 34 liter version should be a great size for UL 3-season trips.
Now a couple gripes about the Osprey Exos design (as pictured). The compression webbing over the side mesh pockets makes the pockets less useful. I like to carry PE water bottles in those pockets. Personally, I would cut off the side compression V webbing, and instead criss-cross the kangaroo pouch with cord for when I need to reduce pack volume. Also, the waist belt pouches look large enough, but once you put on the pack and tighten the belt, they are actually rather small and difficult to access. Some stretch material on the belt pockets would really help in this regard.
And finally, is that a camera/phone/GPS pocket attached to the shoulder strap? If so, three cheers for Osprey, as I have been attaching an aftermarket pouch there for years! Just hope it's the right size?@!