The only thing I don't understand from you guys is why do you think they will have more creativity without being owned my MS?
While making Halo 3, they were easily given a lot of time to make the game, so Microsoft didn't really push them for an early release. Only thing they did enforce on them (and even alone they would still do anyways) is make a Halo 3. Is it MS's fault Bungie takes so freaking long to make a game? They said it was their last Halo game and MS was fine with that. If anything, MS's adverts are what really drove the game and not the gameplay itself. Halo established a Firstperson icon into the console industry, but nothing in it revolutionized the way PC games were like and in fact, Halo was inspired by those creations.
I am not trying to downplay a game, but there really isn't anything too good or too bad about this. While they would loose the marketing genius of MS, they at least get majority of the profits now of any games. I believe, like others would say, they will simply create an alright game, but never at the Halo level. Whether they would create another Halo-esquie game remains unclear, but seeing as it is their baby, I wouldn't doubt it. Only thing I don't follow is why they were being held back in MS if in fact it is the other way around and MS provided them with many resources to get ahead and create their baby.
Perhaps now they may have more creativity, but honestly besides Marathon and Halo, which are all FPS, did they really create anything not related to that genre that stood out?