Amazing but impractical for anything less than heroic.
For backcountry skiing and mountaineering, this is great. But if you're trying to use it for any sort of casual use, it's very much overkill. It is durable like the skin of a rhino, and beautiful to behold, but lacks some basics, like compression straps. The 40 also withholds on a zipper to the main compartment, so you only have rolltop access. 50 and 65 have main side zip. It will last forever, but you definitely have to make compromises when you get a pack that is this directed in its purpose.
It looks beautiful, but just make sure you buy this for the right purpose and reasons.
The ACT fabric will stand up to the worst abuse, the backpanel and fit are easily dialed, it will carry anything short of an elephant with applomb, and construction is...flawless.