What I want, in general:
1. Good, playable graphics. I played CEA, and I was completely amazed by the amazing quality of the graphics they have used. Do that for halo 4, and you've already got a great visible aspect of the game.
2. Good, vast, armor customization. I say almost like the halo reach system. Halo reach provided a very vast system of which we could choose armor to our best likings. Halo 4 could tweak that system, polish it a bit, and perfect it with some additional armor options. Example: I know that many of us want a lot of modifications regarding color, both armor and visor. I've heard ideas for shiny jet black, and bright, flawless white. With visor colors, I've heard ideas for red, green, and dull grey, etc.
3. I think this is what we all want, and is one of, if not the most, important aspect of any game. The campaign. I want it to be long, captivating, challenging, and have a storyline that flows, and is interesting and keeps you on the edge of your seat 'till the end. Make it something we can never forget.
4. One of the main reasons halo is, and will remain at, the top of the xbox franchise. It's interesting, intense, unique multiplayer experience. I want it to have a fair, but worthwhile ranking system, a good server engine, gameplay that will keep us coming back for more, and a great set of playable maps. I know 343 can make it happen.
5. And lastly, (this should be under forge, but I'll continue), obviously forge, custom games and theater. Forge, should have a much wider selection of items and options, such as color. A greater budget, and more maps. This, all makes for a fantastic game, in my perspective.