Usually I wait until the drop before I decide if I like a song or not. For songs with lyrics, I usually listen until I get through the chorus. More often than not, I end up liking the song, even if it's just for something as simple as the title.
I like music to be complicated and I am really attracted to music that requires skill, not just whats catchy or trendy (not saying something can't be trendy AND skillful). Some bands/artists that represent this well, to me, are: TOOL, Unleash the Archers, Adept (the DeathDealers album is sick), Blackalicious, AESOP Rock.
It's pretty hard for me to quantify it honestly, I have an extremely diverse taste in music. I guess it depends on my mood at the time, but a general rule I guess is I want the music to make me feel something.