It's still Hunt Down The Freeman which means it sucks, but it works on Linux.
frequent frame drops
Using the M3SA Dev Build (Access Code: "Password2Short").
It works, didn't experience crashing like previous reports.
Slight stutter, but I've also experienced them on Windows.
While it seemingly runs perfectly out of the box, it crashes randomly rather often and has many bugs during gameplay. One particular map seems to outright prevent your progress due to instant crashing on loading. It's also worth noting that these crashes and bugs almost certainly also apply to Windows due to the buggy nature of the game- so perhaps it deserves a higher compatibility rating for that. In addition, the console font is small and unreadable as with other Source games in Proton.
Crashed after the train level and several subsequent levels crashed on attempting to load them. Frequent crashing occurred regardless though it could be put down to the state of the game in general.
No tweaks needed, but the game will crash instantly when trying to play unless you load the tutorial first.
Performance problems prevent you from playing comfortable.