"In this fictitious world where that game existed," he began, smiling, "its an easy answer: it has to be just the multiplayer experience that we all found in that first Halo 2 game. If you think about what happened in the franchise and what were the hallmark moments when did duel wielding come in, when did another playable character that wasnt Master Chief come in?
"All the things that you and I know about the evolution of the franchise, if youre going to say one thing about Halo 2, youre going to talk about real multiplayer. I think you just have to nail that in just such a fundamentally core way. Frankly [we'd have to do it] probably better than we did with Halo 1 Anniversary. I thought the multiplayer in Halo 1 Anniversary was good, but Halo 1 never had multiplayer in the truest sense, so it always was going to be something different.
http://m.ign.com/articles/2014/03/27/xbox-boss-a-halo-2-remake-would-have-to-nail-multiplayer
This has to be real thing.