Drums and percussion. And I listen for how honest the toms sound - whether I can hear them being struck. Also, does the bass drum have its individual timbre? or does it just sound like a generic thump? Cymbals should have their own location and soundstage. I get frustrated when I hear cymbals disappear into a generic wash of sound, or compressed down to the point where the hi-hat is the same volume as the crash.
