So I tried Steam Play, with the Proton backend, last night. I was able to play BioShock and Kingdoms of Amalur like a charm, and it even mapped my Logitech xbox-style controller perfectly. I don't keep up with the latest releases, so I haven't tried with, say, Red Dead or God of War.
I really don''t know what to ask of #linux #gaming at this point, it's just so perfect. I guess native cross-platform AAA releases would be a nice-to-have, but for my casual gaming, this is a great place to be.