It's hard for me to say, as I don't know/want how to describe music.
I have specific things I listen for and as I get better gear more of the recordings come out. If it'll help, here are the things I listen out for, usually doing an A/B:
1. The decay of the strings of an acoustic guitar. This shows how effective the kit is at retrieving detail.
2. The hihats on the drums. If recorded properly, these are not supposed to have single tones, but almost a "warble" (probably the wrong word) as they decay. Also, listening to ride cymbals, you want to hear the bell like decay, not just an abrupt ending of the note.
3. Stereo image. This is one of the trickiest ones as there are so many factors in the chain that can affect it (as I recently experienced).
So, to relate that to my selection:
1. Sentinal has such a varied "palette" of sounds. It is a reasonably busy piece and it helps to figure out how well your kit handles these kinds of passages. Can you still isolate instruments or does it just become a noisy affair?
2. Crs Craft is nice to me personally because of the jazzy drum solo that the guys do. Also, there are some really nice ride cymbal passages and a fair amount of bristle work on the snare. It is recorded very well and the sound of real drums is a known entity to me.
3. Il Mare Calmo Della Sera - I just like this song for the emotion. It is quite a dynamic piece of music and I listen to possible "screechyness" in Andrea's voice in the opening passages.
These are the things I can think of
