For me it's the singing. I tend to like pretty female voices (think Sarah Brightman) and "interesting" male voices (think Bob Dylan), although there are certainly interesting female/pretty male voices that I like too. Also, a powerful, passionate voice is intrinsically interesting, regardless of its other qualities.
The words being sung are also very important to me. If the songwriter has something important to say, or even just a clever way of phrasing things, I'm likely to get hooked. Good lyrics can make up for a mediocre singer, while a good singer can compensate for mediocre lyrics.
Instrumentally... it's harder to pick out what grabs me. I love intricate, complex drumming; piano & guitar playing that makes you wonder if the player has extra fingers; and energetic horn sections that play off each other as if the players were sharing a brain. But purely instrumental music, while it can catch my attention, doesn't seem to hold it. I tune it out if I don't hear a voice within a few minutes.
The words being sung are also very important to me. If the songwriter has something important to say, or even just a clever way of phrasing things, I'm likely to get hooked. Good lyrics can make up for a mediocre singer, while a good singer can compensate for mediocre lyrics.
Instrumentally... it's harder to pick out what grabs me. I love intricate, complex drumming; piano & guitar playing that makes you wonder if the player has extra fingers; and energetic horn sections that play off each other as if the players were sharing a brain. But purely instrumental music, while it can catch my attention, doesn't seem to hold it. I tune it out if I don't hear a voice within a few minutes.