I agree that commenting on quality of music is very much an opinionated topic; but I dunno...I think a lot of the stuff coming out nowadays is cheap, superficial and all about the money. There is the occasional gem in the mass of average tunes lately; but often it seems like old bands making good new stuff. I like some rap music, but that really depends on the artist. Rock tends to be a consistent performer in terms of quality, but I liked the 90's-2000's hiphop scene too, just had a much better vibe than the current stuff.
Ok, for instance. Take a hit like Smells like Teen Spirit by Nirvana (revolutionised the rock scene), a classic from ABBA or BeeGees, or bohemian rhapsody by Queen; their songs are going to be remembered for a looooong time. Stuff like 'Baby' by the Biebs or 'Spaceship' by that horror that is Minage in my opinion are poor competitors to those oldies.
Being in generation 'Y' people just assume that we should like this stuff. Gimme some Jack Johnson any day over that.