And thus Iron Mal spoke, with the eternal hope that the great unwashed may learn from his wisdom.
Seriously though,
1- No more health regeneration, it was ok in the first Halo because it didn't get in the way, as it stands at the moment most games will fill your screen up with red the second an enemy lands a glancing hit on you, finding cover in a firefight is hard enough as it is, there's no need to jack up the difficulty by effectively blinding me in the process.
2- Knock it off with protaganists in the US Marine Corps, can we honestly not think of somewhere more interesting to pluck a worthy protaganist from? (as for Sci-Fi shooters, how about a good old fashioned Warhammer 40k Space Marine? When was the last time we revelled in being a badass, overpowered demigod?).
3- 'Make your own adventure' games, I'm not opposed to the idea of an open world game (I enjoyed Crackdown) but I do find it tiresom when a game will give you a brief tutorial and then boot you into the big, bad world without so much as a vague idea of what you're supposed to be doing or what your ultimate goal is (famous examples of games with this issue being Oblivion and FarCry 2). I also enjoy the idea of being able to create your own narritive or path (I do play DnD after all) but I think that this has a limited capacity in games since it often feels restrictive (in the case of Oblivion/Fallout 3) or pointless and aimless (in the case of FarCry 2).
I would write more but it's early in the morning and I'm tired.