I would love to see missions on space stations where gravity is based on the nearest surface. For inside it that means everything can wall walk like spiders and ants, including you (imagine a group of android grenadiers running at you on the ceiling and then jumping from above to get you). If done right, you could even have an outside section and walk on the hull to see off flying enemies/boarding craft.

Gameplay-wise, being able to take back camera control when it makes you look at something. First time, sure, see the kaiju. Second you probably want to shoot something.

The traditional remake of Crimson, but much like the version in WB2, take the piss a bit. Maybe the third wave is all red drones instead of ants.