So, as far as i know, halo 3 odst is going to be a campaign and recon party for those either involved in the story of those who want MAOR RECONZZ PL0X. But the campaign and armour were never the best thing about halo. So im going to list the things that make halo great and say how halo: odst could improve on them.
Customisation: forge on halo is not only new, it is goddam awesome. New maps made every day? Its every players dream. So why limit the mapmaking tool to maps? I would love the ability to place brutes, grunts and more in the maps. Fighting of the endless ever-growing horde of brutes or laughing maniacaly as you 'burn their mongrel hides'.
Gameplay: What can i say? Just keep it the same with better graphics, i dunno.
Epicness: I don't know about you, but i sure think big ass lasers are epic. So why not have a load of players facing off against each other? Like use a sooooooperdoooooper computer to allow players to have 1000 on 1000 battles on a plain empty field. Like 1 life, and when that player dies, another is randomly invited. (he has to be in the main menu)
Theater: Make it easier to use and add a option to sake the screen so we don't see all that crappy shaking in machinimas.
Kickass moves: Make the odst have a goddamn reverse kick thing that totally owns.
Basically, make halo odst more than just campaign. Improve on the special features that make the game what it is.