Things i would like in a Batman next gen game:
-Open world, Free Roam
-Expanded combat
-Realistic gliding (ex. jump from a tall building, glide long distances, jump from a small building, shorter distance gliding)
-use of gadgets (when i say this, i mean in a sense, you take enemies out with your own means, not something that you have to wait for a message to pop up so you can use a specific item)
-Crime solving (ex. instead of asking pedestrians like in SM2, Batman's radio should be linked to Gotham Police Department, so he can hear the dispatch)
-I would like to see the missions done random, like in the middle of solving a crime, you see the bat signal on, indicating another story mission.
-playing missions as Bruce Wayne, this should be an option during some missions, if a mission requires you to gather information, you should be able to go as Bruce Wayne or disguise yourself to look like a general thug, and gather information before taking the target down.
thats about all i can think of now, if i get some more ideas, i'll be sure and post them