A lot of factors come into play here.

The complexity and originality of the music comes first and foremost. I like pieces that are in awkward or changing time signatures for example. The standard verse-chorus-verse-chorus format of today's pop music doesn't usually cut it for me, and a too-repetitive beat will leave me bored.

Good instrumentation is probably second most crucial. I prefer bluegrass instruments like banjo and violin as well as Latin and African percussion (not necessarily at the same time of course xD). I also like blues and jazz instrumentation. I don't typically care for electronic sounds, although computer generated "noise" has its acceptable uses.

All other things are of lesser importance, but still matter some. Proficiency of instrument are voice matter only to the extent that it can ruin a song if it is really, horribly bad. Lyrical flow and word choice are things I highly appreciate but I can still enjoy a song with simple lyrics.