MG Online is still popular, i presume. my friend still plays it from time to time i guess.
Warhawk (based on the demo only) is still kinda popular.. if you only wanna play with about 5 people at a time. or it could have just been a bad time. i think there's a second warhawk out? i dunno. check gamefaq's boards before you buy that one for sure.
no clue about the other two, but i think there's a resistance 3 coming out or something. no clue.