I'm the same way; one thing I loved about Halo CE in both campaign and MP was the sense of isolation and loneliness. It was you vs the world and you felt the gravity. Now, it's more like some cheesy summer bromance blockbuster.
Solemnity has turned into haughtiness. Simplicity becomes tortuous.
I'm not talking about isolation and loneliness, those are not things i miss (but i would not oppose returning them either).
It is just that when you portray war, fictional or not, i'd prefer it to be disgusting in many ways. Black and black morality, you know?
Show the Covies to be truly genocidal, yet at the same time, make it clear the humans are seriously considering returning the favor. Make the Covies terrifying enemies, yet humanize them some (that Elite you just shot "dead"? What if he were clearly pleading and would be terrified of you?) (I mean, seriously, don't say the Elites don't feel fear. All sapient beings probably feel fear as it is damn effective survival mechanism)
All with much more gore than Halos have had (strong visual impact, i think. In theory. Me, i'm not one bit disturbed by gore in games (or TV or film) ever, and that disturbs me...). There is no clean death with powerful weapons.
And this should extend to the multiplayer as i said, though some things don't work there nearly as well, by the very nature of it.
EDIT though showing you're very much alone in the war might be good, i think.
EDIT2 for the record, i don't think the Halo games portray war very well. Unfortunately. For military science fiction....
EDIT3 though it occurs to me that many military SF works don't actually portray war that well... ARGH, this is one of those things i should not think or it starts bothering me a lot.
Fucking English language. After Halo 3...