On a few occassions, fighting the snake would slow to around 10 fps. That same scene would be fine at other times so it seemed like a random problem.
Crashed every time Mantis was my opponent. Never crashed at any other time.
If you have any tolerance for an occassional crash, you'll enjoy this game as much as you would on Windows. As mentioned, for me it crashed every time Mantis was my opponent, but every playthrough draws randomly from a pool of possible opponents so it was fine when he didn't come up. A playthrough is short enough and the game loads quickly enough that i don't think it was a big deal. I beat the game 100% with all characters so it can't be that bad.
Default Proton worked but then didn't work after a Proton update so i forced it to use version 7.
I tried older versions of Proton and it did NOT crash when facing Mantis, but my XBOX One S gamepad wouldn't work, and it wouldn't go fullscreen for some of them. One Proton version only showed a black screen.
Also keep in mind with this game that Windows users commonly experienced bugs so there are some minor non-game-break bugs that come up but are probably common to everyone.
On a 1920x1080 monitor part of the game was displayed in the top left corner and the rest of the screen was black. Most of the gameplay area was not visible making it unplayable.
Graphics displayed perfectly after forcing Proton 3.7-8 in compatibility options. Other versions tested (Experimental, 7.0-3, 5.13-6) did not fix the display problem.
There are no resolution options in the menu and the game runs in fullscreen only.
Game can crash randomly, cutting short your current run. As this is an arcade-style fighting game a full playthrough can take around 20 minutes so not much progress is lost.
Crashes don't seem to be Proton related, Steam forum users report similar issues under Windows.
Completed a couple of playthroughs, apart from issues detailed above there were no problems.
Keyboard and gamepad controls both work great. Multiplayer untested.
Runs without issues now even in fullscreen
The previously mentioned issue of Cinnamon taskbar being visible appears to have been fixed.
The game works fine without issues except that the Cinnamon desktop taskbar is visible at the bottom. Game runs in a fullscreen borderless window. There are no settings in the game to adjust resolution, aspect ratio or switch between windowed or fullscreen. I'm rating it silver because can't tell if this is a problem with Proton, Cinnamon desktop or the game.
Insists on running in a fullscreen window with my (Cinnamon) taskbar visible, otherwise runs OK. Moderate slowdown at points, but not significantly worse than native.
No music and playing with a controller the directions get stuck.