People can probably name more stuff, but for me, I'd like to see toggle options for two things in Halo 4: assassinations and hitmarkers.
I've explained assassinations, and I've explained my position on hitmarkers, but at the risk of getting annoying and repeating myself, I'll do it one more time. One of the problems I have with hitmarkers in a Halo game is that they're slightly superfluous for multiplayer. Halo games (AND Halo 4) have such a good feedback system in shields with their popping and flaring that I don't see hitmarkers necessary. But that's more of a nitpick than anything.
My main problem with hitmarkers comes with their inclusion in campaign. Hitmarkers scream such a multiplayer aspect that to bring them into campaign might be detrimental to the campaign experience in that it makes the experience more like multiplayer. I know I've been the only one to bring up this point, so it may be just me being silly (or stupid), and so I can understand why hitmarkers are in there. In campaign, too, Halo has had such a good feedback system (Halo 4 looks to continue this trend too) in that enemies react well to being shot – their shields flare up, they flinch – you know, the works. So even in campaign they're a bit superfluous. It's almost like they're a substitute for better feedback, you know?
Of course, I haven't played the campaign yet, so none of what I brought up may matter, but that's been my experience in other games. And I think I'm the only one who has had any problems with hitmarkers being included, so I guess I'm just crazy. And when looking over the entire game, the inclusion of hitmarkers – however I feel about them – will probably amount to little more than a nitpick anyway.