I'm gonna be a lot different than other people here. Lyrics and sound are equally important. In order.
1. Lyrics. I need to feel like there is some sort of story, some kind of emotion, or some kind of statement. Or at least some good rhymes, good use of words, etc.
2. Guitars. Solos are almost essential in metal. A good tone and good guitar parts are excellent.
3. Drums. The more complex, the better, and the more creative and unique, the better.
4. Beat. A strong, focused beat, something powerful and moving, is very important.
5. Bass and keyboards. The tone of keyboards are very important. Also, bass must be present and noticable in the EQ.