So far Disco provides best gameplay opportunities.
Moreover I won`t accept any game with OOC anymore...So if I were you I`d go Assault cube, Wolf team (no need to RP), LD2. Also, if you want RP - take a look at fRPGs
Awesomenauts, Team Fortress 2, I hear that Chivalry is good but I have not played that yet, I have fun with the Napoleonic Wars expansion for Mount and Blade, Tochlight II if you have some buddies and want to dungeon crawl, and there is always Borderlands 2 I suppose
But it would help to know what you were interested in
i quite like Blacklight Retribution - free-to-play fps on steam. Sure its pay to win, but the shooter part is solid and the graphics pretty if you've got a good computer.
Borderlands 2 is great in coop. Only played it split-screen on console and it was a lot of fun.
I haven't tried Torchlight 2 in multiplayer yet, but its a lot of fun in singleplayer and I heard good things about the coop.
All of the games you suggested are good
But i have some Problems..like......World of Tanks my connection Speed is 1M so It would take years to download it
and some Games aren't available in Syria ( Yeah....I live there)
I tried to Play Section8: Pejudice , and MW 3
but both are cracked so i have some Problems with them