Khalil's_Black_Excellence
The King of Fighters
That new God of War game might kick that off for this genre. I won't pass judgement on it til I see it in action though.
Thing is, I'm not exactly thrilled or looking forward to MP in a GOW game, simply cuz thus far, the story hasn't really had any sensible way to seem to make that work, as Kratos doesn't trust anyone and never has any buddies and whatnot. Like you, I won't pass total judgment till I at least see it in action, let lone play it myself as well, but I think it'd be silly having like 3-4 people all playing Kratos. I never liked MP games to just have everyone controlling the exact same character.
Batman on the other hand, already has an established relationship of allies and they've already allowed you to control them in the most recent game, so it makes a lot of sense already to have them fighting alongside with him and that'd be much better done and more fun with another human than an A.I. controlled assistant. Technically speaking, it makes even more sense for Batman to have his friends help him this time cuz realistically speaking, if Batman was to take on as many of his main enemies alone in 1 night as he does in this game, he'd quite possibly not make it out alive.
And they could easily incorporate this to work for both online and offline, as the fighting challenge rooms could be done offline and the more grand scale ones of like using the city could work with other players being Robin, Nightwing and Catwoman. I don't think they could lose going this route, as long as they put the same level of craft all across the board.