I want Halo 2 exactly as it was. Don't get rid of the button glitches, don't get rid of the super jumps, not getting out of maps, not the banshee launch, etc. Update the graphics, maybe some new maps, do not add armor perms, do not add equipment or armor abilities, anything of the like.
If you go over to the Reach forum, everyone says that Halo 2 had the best multiplayer. Correct me if I'm wrong, but I also believe Halo 2 had the highest online population(though, mw1 and mw2 weren't out).