When you listen to a song, what's your most important factor in determining if you like the song or not?

For me, in this order:

Guitar
Vocals
Drums
Lyrics
Lyric meaning
Video

Hmm... well, the "catchy" factor is always there. If I find myself humming a song, I more often than not like it.

Other than that, I'm not really specific and can't prioritize my likes on music, I just like what sounds like what I like. (funny sentence, no)

The extent to which it causes my face to change expression.

1.sound

Judge:

Can i totally freak out to this one?
Y / N

1-Rythm
2-Sound
3-lyrics

1 Beat
2 If it gives me goosebumps

Some of them, when applicable to the genre:
1 - Lyrics: concept + theme + message + meaning + complexity/simplicity of rhymes and its effectiveness (I like to see multisyllabic rhymes and figures of speech) + congruence
2 - Creativity: originality + delivery + deepness + footprint
3 - Instrumental: variety + drum patterns + broadness of scope + execution + quality/richness of sampling + atmospheric density + feeling or adrenaline + rhythm.
4 - Credibility: Sincerity + ability to evolve + passionate artistic purity (although subjective, I do think that the vast majority of heavily commercial music sounds tendentiously mediocre, artificial and lack in passion)

Those are some of the main characteristics I evaluate when I listen to music.

what the? i just listen to it if it's i like then i like it, don't really care why.

I feel the same way, I can't stand listening to Jay-Z, Lil' Wayne, or ANY commercial artist, it makes me sick, I only listen to, and support Underground and Independent artists.