As far as sound goes, there is at least one thing devs can do to dramatically improve the sound quality of their games: live soundtrack recordings. No more of this midi and synthesized shit, at least in the AAA games. Use real musicians playing real instruments.
I know some people feel that in many cases the synth music is adequate, but anyone who has played a game with live music should not doubt the impact it can have.
Just compare this to this. Or this to this.








