Skill gaps. In Halo 3, if you were a sergeant, you would always be paired with other sergeants or close to that skill in matches. In Halo: Reach, I am currently a Commander g2 (haha I know, low rank but whatever, didn’t really ever like multiplayer other than the maps powerhaus and sword base), carrying on, I am a Commander, but I get paired with INHERITORS. I mean really. Why are they pairing me with such low-skilled players? joking lol 
(the joke is here for the reason that every higher rank iv’e met hasn’t been particularly good…). Anyways, Halo 4 needs a better skill system like older Halo games. If i’m a rank 5, put me in a match with ranks 4-6. Not rank 30s’. Look at MW3, I’m not good at the game, yet I can never learn how too play because they put me in games with 10th prestieges. Don’t do that. This should be the most important aspect for multiplayer. In Halo 3, there was a sort of boot camp for new players, bring that back. It would be cool too if there could be a buddy system, where a new player is paired with a high skilled player, an the old player teaches the new player in a match. Something like that would be great. Any thoughts?
I think having a good network setup would be the most important.