Verify Integrity of Game Cache...
More than likely, you are having DirectX issues. Try the following:
Set Launch Options...
Some servers use Pinion advertisement, a buggy plugin that sometimes crashes TF2.
Note that some servers require you to watch the MotD for a minimum amount of time (e.g. 30 seconds)
C:\Program Files (x86)\Steam\
Once the game has loaded and the FPS have dropped below playable:
From here on, the game should increase dramatically in performance.
To increase performance:
Cinnamon, by default, skips the compositing rendering manager if an application runs fullscreen, which in turn, disables Vsync. Enabling the compositing manager turns ON Vsync and (depending on the system) slows the game down.
Anti-virus software can interfere with a file in TF2's folder, which gets updated constantly during gameplay.
C:\Program Files (x86)\Steam\appcache\stats\
C:\Program Files (x86)\Steam\SteamApps\common\
Alternatively if you are using -noborder -window or just windowed mode:
Enable developer console (~)