I'd love it if they redid the campaign. Halo 2 was a fantastic story, the best in the series, but it just looked shoddy and rushed. But if you put that story with the amazing artwork and graphical ability of the Halo 4/Reach engine, it would be the prettiest and best told story of the entire series. I would love multiplayer, but my guess is that if the remake happens at all, they'll do it similarly to CEA, and just select a few of the most popular maps, and make them part of the Halo 4 (or whatever Halo game is out at the time) multiplayer experience.