I think this is what is so good about online multiplayer. Take a game like COD for example, you've done single player, you've played against your friends, but the best part, which you can do over and over again is playing online. I would say that most games with online play have great re-playability. So Battlefield 3/4 and things like that. TBH I hardly even play single player at all! I just play my games online over and over.
Saying that, I am bored of COD, and gave up on it a few years ago. That's more of a fault with the games all being the same. But similar games like Battlefield never get boring for me. I think GTA is a good game to keep messing around on, but depending on how you play, you can get bored of that too.