I want a much more cinematic experience for single player as well, but mostly multiplayer. I want to feel like I'm in complete control of my Spartan. For me, it's the little things. In Uncharted 3, the main character Nathan Drake put his hands on walls when he got near them-he reacted with his environment. And in ACIII, Connor reacted with his environment as well, reacting to inclines and such. I feel like the multiplayer hasn't fully represented the Spartan's capabiities. I know there will always be technical limitations, but it would be pretty cool to see your Spartan dive behind walls and cover, jump, roll, and slide over things in the environment, and maybe even have a slight knock back or view disortion when next to something exploding. I know that in Brink, the parkour elements looked rediculous and awful when seeing someone else do it (from a third person perspective) so that would be a major issuer I understand. But I think the little things-from grabing and pushing walls while sprinting to even animating more visceral movements and actions-would make all the difference. I see cutscenes as a disconnect from the player, because you see the character you control do things you aren't able to do in game. With a more cinematic game style, the game would become more immersive.
Another thing I would highly enjoy is larger, grander maps. I remember the greatest feeling I had from Halo 3's multiplayer was when someone would drive the Elephants (something else that should be brought back in some form or another, personally, I'd love to see it's Halo 4 variation from the campaign intergrated into a large map) all around Sandtrap (another perfect map, just so you know) and everyone would jump down from above and we would have massive battles all around, and it was great pure fun. I'd like to say it was one of the few times in multiplayer that no one was mad from dying or felt cheated or cheaped out, because everyone was enjoying the sheer madness of two elephants driving side by side or going head to head in the center of the map. Now imagine even bigger vehicles, and larger games. Imagine a Scarab destroying the evironment while players are boarding from vehicles and on foot and having massive battles on this (or perhaps other) giant vehicles and trying to get control of this massive ultimate weapon. I know that other popular reccommendations include the pelican. With large scale maps, you could transport a lot of other players around, and perhaps even make it a variation of the Battle Pelican in the Halo 4 campaign to fight other air vehicles or other large war machines such as the Scarab. This could become a great challenge, but no doubt would be an excellent innovation to the franchise that would be sure to hook people in even more.
Another big thing is forge. I mean no disrespect, but it would appear as if the different forge types (3, Reach, 4) are more innovations than actual improvement. There, I said it, and I am sorry.
Anyways, my friends and I were surprised by how much we truly missed Halo 3's forge, frustrations and all. I don't have too much to say about forge, but I'll just say what prevented me from some awesome game types in Halo 4's Forge:
-Infection. That about sums it up.
-Teleporter velocity: When you go through teleporters, you continually go faster and faster. If you're wondering why that is a problem, I'll explain my game mode idea to you. Basically, you spawn in the air with vehicles and turrets falling all around you. (this is the space level by the way, sorry I forgot the name) and then you fall to the lowest possible point in space possible then you get teleported straight back up to the top. The idea was to have a crazy gametype where you would kill people in the air and board vehicles and hijack-all while continusly falling. This doesn't work however, because you gain speed so much that you eventually can't do anything or even see anything. It's a little problem, but something I wanted to bring up.
-Fixed Man Cannons: This also hurts gametypes such as Frogger, where a Scorpion Tank is in the middle of the map and the objective is to kill him (Originally an infection game type) and you had to drive vehicles through man cannons to land on different platforms with the danger of falling to the bottom of the map and dying (This was on Sandbox in Halo 3) The fun in this game was that you didn't know whether or not you were going to make it-the man cannon was as unpredictable as your fellow "team-mates" (a lot of team members hilariously made sure that some people didn't make the jumps). With a fixed landing spot in Halo 4, you're ALWAYS going to make it, you're always going to land in the same spot.
-Weather: Kind of self explanitory, it would be nice to affect lighting, clouds, rain, water, etc. I know they're two completely different engines, but Far Cry 3 has an excellent custom map editor.
So now for cutsom games. Beyond Infection, there's some stuff I'd love to see, like and ammo capacity, specifically how much ammo a person gets. Imagine the game types that would utilize a one bullet scenario.
I admire the customization in Halo 4, but still, more is more, so I would like to see even more. Not more amor persay, but actual more options. More specific details of every aspect of your armor, heck, maybe even fully customizing your armors look from the ground up. How your visor looks, different shapes of your helemt you can edit and so on. That would be very interesting and amazing to see.
Also, I don't know the capibilities of the next gen Xbox, but having bigger battles, like I don't know, maybe 16v16 or even like 20v20 would be interesting if you made it work.