I want to hear any type of metal that doesn't suck theoretically. Song/artist or artist/song, whichever is proper.
A few artists/bands that I like:
Dream Theater
Dragonland
Nightwish
In the metal genre, I have heard the good, bad, ugly and genius. It seems that the bands whom suck consist of this:
100% energy and 0% concept
Minimal instrumentation, unless what's being done with the instrument is
I like screaming, but not completely pointless and uncreative noise, especially if it doesn't sound tuned (because if it does sound good, then you'll wonder why they're screaming but you might like it anyway)
Nothing but the same constant audio effects and power chords, no other music (treble) unless you're at a break/rest or something, but for the whole song? God no, gimme some treble.
Old, generic, uncreative and overused concepts. If I like a song with these elements, it must kick some major ass.