Personally I’d revive Begone (Nplay.com). It was an FPS game built on Unity engine. I would to play it one more time just to feel the GUI, the servers and the community again. They had cool account systems and forums aswell.
Honourable mentions:
Minibash (a spin-off game to the game Toribash)
Fly like a bird 3 (gamevial.com)
And Attack on titan tribute game(Feng Lee)
God Hand (PS2), a great 3D brawler / beat 'em up, somehow the genre is in decline and haven’t heard of any games tried to repeat God Hand’s style.
Conflict series (PS2), like Conflict: Desert Storm and Conflict: Vietnam, it’s a squad-based third person shooter, you control 4 characters at once, amazing couch co-op experience. Sure we got Ghost Recon nowadays, but the squad control is surprisingly shallow compared to Conflict games, you can’t even manually control them.