Whenever you're ready to get to the next level you should try Enemy Territory: Quake Wars. Preferably the PC version.
ET:Quake Wars is a lot more advanced than normal FPS-games when it comes to leveling up/upgrades and also the tactics and team-play
(but doesn't have the steep learning curve of tactical squad based shooters á la Ghost Recon which I don't like at all).
The upgrades in ET:quake wars are only active during a 3 map campaign, then reset, but I think that is more fair.







