Improve the combat and make it much harder, and I'm in. Also, they reaaaaaaaaally need to reintroduce the fear mechanics of Arkham Asylum. If they made Predator areas, along with the challenge maps to accompany them, much bigger while making the enemy ai more sophisticated and high in numbers, could make some incredibly interesting stuff.
Imagine picking them apart, and having a wide breadth of reactions from each guy in the room. It'd be awesome if you could do like Batman did in the comics, and play some psychological games with the enemies. Hang guys in painful looking poses so when someone turns around a corner and sees them, they shit their pants and run, or maybe become more paranoid and end up accidentally shooting a squadmate before you take them down too.
Chills.