Reaper of Souls was on sale recently so I picked up two copies hoping it will runs as well as Diablo 3...
It runs great!
I previously posted a Diablo 3 guide in PlayOnLinux which still works except now you can use Proton GE:
Continue into Act V and then enable Adventure mode. Use your favorite character and crank the difficulty up to Torment... slay new minions, mini-bosses and new BOSSES! Fight through heaven once again and stop Malthael Angel of Death! Blizzard has out-done themselves again! The levels are more detailed, more interactive, enemies are clever and fun to kill! I can't wait to try Adventure mode.
As expected, Reaper of Souls runs really well with Proton. I did have to add the argument: -d3d11legacy
This allows Proton to handle the DirectX 10/11 compatibility. Battle.net also is running in Proton GE so we were able to play co-op without a lot of work. Glorious Egg Roll does it again!
Mint 20.1 64-bit
GeForce GTX 1060