By storyline, I don't just mean the plot, but how you can interact and alter it's course. I've always wanted a more complex storyline to accompany a Halo game, with deeper moral conflicts, and actual choices to make and such, as opposed to the simpler, clear cut morality we've seen in the past games. Sort of like a Bioware RPG. I knew that Bungie wouldn't stray too far from it's linear storytelling (ODST was still rather linear, as all paths lead to the same outcome), but now that Halo has been "reborn", so to speak, I have faith that 343i will try something new with the storyline. I know that many of Bungie's staff are now a part of 343i, but still, I believe that this is a rather ample oppurtunity to venture into unexplored territory, and that 343i will take it.
My problem with that, however, is that it will break the "silent-protagonist" image that the Chief has maintained for so long. Oh well, the point of his silence was so that we could fill in the missing personality with our own, and more decisions will do that just fine.
Regarding the new leaks, it seems that 343i may be headed in this direction, with opposing human factions and whatnot. If you haven't seen the leak already, here you go.
http://segmentnext.com/2011/06/09/halo-4-leaked-plot-features -and-gameplay-detailed/
Anyways, what would you like from Halo 4?
Oh, and this new alien threat probably won't be the flood. If it is, however, I just might snap.
[Edited on 06.26.2011 12:36 PM PDT]