Like everything else in the world, there is good rap, and there is bad rap. When it's good, rap is great. It can be really beautiful, and really moving. But when it's bad, it is shit. Obviously, you're not getting a good picture of the totality of a genre of music if you listen to a Nelly CD.
I could list dozens of great rap acts, but it's not like anybody here cares, so fuck it.