You know what I really don't like?
When game developers mix down audio into a master mix. When they take SFX, VO, Ambient and Music and pin them together instead of allowing the game to sync them up and using the engine to apply modulation to the audio.
Games like Halo are really good at letting the engine do the audio work. Valve is mostly okay, although certain very awesome parts of the game's music are actually part of a master mix (Portal 2 is the most frustrating).