Music needs several things for me to really like it. But, before I start, I'd like to say that for me, it doesn't necessarily need them all.
Lyrics- The lyrics need to either mean something to the artist/band or to yourself. It also could tell a story of some kind. I also love it when an artist/band has lyrics for you to interpret yourself. Tool are especially good at this.
The style of the vocals- I'm not really picky about the vocals, but I really don't like Death Metal, 'Hardcore' or nearly anything with growls of any kind. Exceptions to this rule are Dir En Grey, Cradle Of Filth, Slipknot and Gojira.
Instruments- Personally, as a guitarist, I love songs with really good guitar riffs, solos or just good guitar work in general. I'm not picky about the kind of instruments. I also like synths and other electronics.
I can give anything a chance, but these things define how much I like the song.
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