more customization of your character and variety.
something sort of like the Hitman games where you're an assassin/mercenary/thief/etc but FPS/3rd person and a lot more weapons and ways to kill people. better use of the environments, etc.
a game where its truly open ended instead of like 3 entrances to a building but you still have to kill the target with a gun. Like you could wait for day or night, you could rig his car to explode, snipe from a distance, disguise yourself and get in close with a knife or garrote, or just sneak in, or even just poison his food. Or hell, rig the building to explode or something.
you would have tons of different missions to take. like to assassinate a person, steal an object, escort a vip, etc.
Something more realistic where it doesn't take many bullets to kill an enemy and the same goes for yourself too.