As a hip hop head since I was 10, performed it, written lyrics etc. etc rap was one of the best and worst things to happen to music.
Best because it introduced a vibrant new sonic artform that at it's height is an innovative, powerful and beautiful auditory force.
Worst because unlike other music forms where you have to at a minimum be able to carry a note, play instruments, etc. all one has to do is just say words over a beat. This has lead to terrible quality control, and minimally talented "artists" being able to take over.
Yes, there is bad music in all genres - but I've always said hip hop is the easiest music to do, but the hardest to do well.