-I want to know what happened to the Arbiter and the Earth-friendly Elites. Their story can't be over.

-Covenant (and other enemies?) speaking english. This was a big part of what made H2 and H3 so fun and replayable, and it made each enemy feel like an individual with a past and future, rather than just guys to shoot.

-Brutes, and all their cool toys.

-Dedicate graphical budget to huge, expansive environments (even if you can't explore them), lots of AI in every encounter, and really pretty effects like water, explosions, rain, fog, etc. Basically what was done in H3 and Reach. H4 had really nice-looking character and object models, but the environments were static and confined by oppressively close sky boxes.

-Don't give up on Prometheans, but sort out who or what they are. Right now their backstory, visual design and gameplay role are contradictory and seem like they were developed independently.

-No more genetic magic of destiny muddying up the story, please. Yech.