Gamer Groups! Clans! (Seriously, wtf, Xbox? FACEBOOK has better group support)

Official scripting access for gametypes. (the hive-mind can improve your game immensely - if you let it!)

Firefight back, as a full-on, no-holds barred survival mode (ODST with reach+ customisation, and continuing difficulty escalation.

Boldness and clear, well-defined and delimited goals for modes. (spops was too envious of campaign, and too disgusted of it's Firefight heritage)

More, interesting skulls/modifiers (and you can get rid of the blind skull)

Lifetime challenges (e.g. Legendary, LASO, no deaths on levels, survive 7 sets of standard firefight)

Personalised challenges (e.g. not everyone has time to rack up 400 double kills in grifball, mate)

Weapons that don't need tweaking every few months (they're seriously going to tweak it AGAIN)

More unique weapons. If you want customisation go ALL-IN on that for the human ones: where it actually makes some sense! (steampunk promethean liveries are just... bleh)

Better gametypes (seriously, dominion playlist is getting axed, yo. Speaks for itself)

If the Prometheans come back then they need to be completely re-thought to differentiate them better from Covies. More powerful =/= better enemy.

Drop the stuff about wargames being canon because it never made sense, was poorly implemented, barely referenced and made even less sense as Halo 4 has gone on (magnetic risor fields, I mean, really?)

Story wise I hope Chief hasn't turned into a broken, pathetic mess searching for 'what it means to be human' and I hope he doesn't magically bring Cortana back from the dead. That would be uber-cliche.

I hope Infinity running an utterly pathetic campaign on Requiem, with no overall goals, massive casualties, severe security breaches of the capital ship, having only 1 effective spartan (Crimson), and almost getting sucked into a star means they'll learn an ounce of humility and drop the 'NOW WE'RE THE GIANTS' *rams cruiser*, arrogant BS.

*breathes*

Ya know, just small stuff ;)

(p.s. list is incomplete)