CoD4 has good multiplayer but the campaign is short and there is no co-op.

R6V2 has co-op, a long and intense single player, terrorist hunt, and multiplayer.

R6V2 sounds like ur game to me.

If you really like it difficult play on realistic, I got halfway through the game thinking it was on normal and realized I had it on realistic, theres no way I can go back now.