Case in point, I used t' play Assassin's Creed: Revelations multiplayer somewhat competitively. Naturally I switched t' AC:III when it came out, but I went back to Revelations for some time since AC:III's multiplayer doesn't work half the time. To get my AC fix I flip-flopped between the two regularly, and despite the games' similarity to each other, it really hurt my performance.
And yeah, CoD 'n GE still have active communities. How active I wouldn't know, as I ain't a part'a either.