This is sort of a general post for the halo franchise though it obviously most accurately applies toward future Halo titles, in this case Halo 4.
Basically, this is a short point, but I think a big one.
Halo needs more story telling.
I think Halo does a pretty good job at telling it’s story, but not nearly a fantastic one, especially since its actual story and details within them- the games and books- is fantastic.
Half Life 2 and Uncharted both are good examples of nearly the opposite- quite good story telling, with run of the mill surface level blah stories. However, they are told well and people start to think the story is good.
Halo 1 had good story telling, but was a bit shorter on content. Halo 2 did well in both. Halo 3 went short in the story telling, opting to shorten their cutscenes while possible. ODST and Reach I felt had better story telling but the stories themselves weren’t as good.
Now, what we need is a return to the Halo 1 mystery exploration with the Halo 2 level of detail in storytelling, particularly on the covenant side- though whatever it may be. The terminals to Halo 1 are a good example of things that Halo 4 should implement, but I think a more direct story with many more cutscenes and segments such as the very intro to Halo 2 where you walk aboard the tram, etc. and the covie cutscenes are what Halo 4 needs. Do this, and also do it in abundance.