Hi all. I'm on a new install of Debian Stretch, with XFCE. I have 3 issues with running the Linux version of Source games (I have tried TF2 and Portal).
(1) The games are continuously quite laggy (feels like < 30 FPS), but the FPS is a constant 299 even during the lag. I tried VSync (60 FPS) but it didn't help. My ping/internet is fine. I don't get this issue on the same PC on Windows.
(2) The colours/textures etc look worse somehow than on Windows (poor detail), even though I'm running the game on all max settings at the correct resolution (1920x1080). It's hard to articulate how it's different but it's just worse.
My mat_dxlevel is at 92 (the maximum available). My screenshots in Linux version of TF2 follow (first two have different Gamma setting to last two) :
https://imgur.com/a/Abxqk92
https://imgur.com/a/CeXdWMm
https://imgur.com/a/eQ9kwXy
https://imgur.com/a/0Vf8i7H
My GPU is a GTX 1070. I've tried the normal Stretch Nvidia driver as well as the more recent Stretch back-port Nvidia driver (390.77), but the problems are still there.
(3) Some of the text in the game (eg. chat) is a really small font. I installed ttf-mscorefonts-installer ; that helped with most of the fonts but not all fonts in-game.
