Imo colour needs to improve a little. I am getting tired of the brown and grey, and also for some reason I don't really like bloom either (though maybe that's just me). I would be very happy if this could be achieved while attaining 'realistic graphics'.
Gameplay-wise, really, good gameplay has existed for years, I don't think it's a matter of improving, or progressing, but rather finding new mechanics. Obviously the only thing that can improve then, is good controls and less bugs.
ALso, I guess AI needs work, but I generally don't mind cheating AI, can potentially give the game more challenge than it normally would have.