Ok, I think I may have discovered one bug. Setting full screen in the options instead opens up a window that's the size of the screen. Haven't seen if this behaviour exists in Windows yet.
Fullscreen bug still exists as of Proton 4.11-12. Since the initial report, I've upgraded my system (see gist).
Here's a log when enabling full screen mode:
steam-511680.log
Fullscreen bug still exists in 5.0-3
Not sure if this is KDE's doing, but launching the game always makes the motherboard's PC speaker beep
proton 4.11-12x1 2020-01
Haven't experienced any major issues as of yet.
System specs: https://gist.github.com/archaeme/ff2422529d68ed149f3b148161b9c698