I started playing 2142 + Northern Strike again recently - man is that game fun. They really hit the nail on the head with the unlocks, ranks and achievements too, so the curve isnt too steep like in BF2 but isnt too easy as to have everything gained in a week. Not to mention the fact that the game play is excellent, i'd never really tried to go sniper before as the head collision detection always seemed a bit off.. for some reason im really enjoying it now.
Aside from that i still play TF2 and forged alliance from time to time.