I find that around 80% of music sounds "good", for the first 30 seconds or so, this falling to around 50% as the song goes on, because sometimes the song gets annoying.This applies to rap songs to indie to pop or whatever.
Wherever i like it is an entirely other matter. Firstly i ask myself does it sound good? If it does, then i ask myself how good the instrumentals and vocals are? Are they complex and interesting? Do they create the appropriate emotion? (Most music stumbles at this point) I then ask myself if the lyrics are good, are they meanigul and interesting? How well do they go with the song? What is the ultimate "point" about the song? How original or interesting is this song? (believe me, a LOT of music lacks any point at all)
If it passes this test, i like it. Sometimes if the instrumentals are really good but lyrical quality is lacking i will still like it, based on instrumental quality alone. However, a band which combines innovate and interesting lyrics with suitable instrumentals and vocals will always be superior.