Despite how much RE4 had packed into it RE5 still has so much potential for new things that could make the experience even better.
I think it would be neat to have more "Ada's Assignment" type unlockables so we could get story details from the other character's perspective.
Have to keep the interactive cutscenes (Qte? What does that stand for?).
More weapons and enemies is a dur. As well as more interactivity with the environments.
Maybe let other character be interactive. Such as we could've had a level or two to play as Luis, although you could just have saved a bonus level as "Luis' Assignment"
I mean, I can say "more, more, more" all I want but the real aspect lacking in RE4 was it's horror factor- so try to work that in as well as keeping the intense action.
Man, I don't even want to think about RE5 - the possibilities are endless and it's too damn far away.
EDIT: Oh I forgot to mention where I'd like it to take place - which is a huge, huge factor. I liked the idea with the White House. I was also thinking more of the village's woodsy type of areas. And maybe it could take place during the winter and you can see invisible enemies footprints and stuff. That'd be neat.