Well I think that "damage simulation" can be improved significantly.
For instance if a bullet hits the leg the character/enemy he/she/it should limp, bleed, and move differently.
Swords/blades should actually cut or dismember the enemy/character even at first hit and should not pass through objects/enemies as if they were made of air.
I liked what Rocksteady/WB did with MrFreeze in Arkahm City/Origins.
The idea that the same attack can't work twice on a enemy/boss it's very good IMO and possibly more feasible than develop an actual "learning AI".
It would be like playing against the Borg but without the hive mid that it's bad in games
Interactivity should be improve as well.
Manipulating objects in the the environment or even the environment itself it's something that too few games did.
"Organic HUD" should also be a nice improvement...yeah I know I said it already many times.
Dead Space, Crysis series, Syndicate, Ghost Recon:FS, Metro, MGS:GZ, The Division and lastly COD: AW all show that HUD can be done "organically" with not detriment for playability.