Yes, there is. Some music is masterfully and painstakingly constructed. Even if you don't appreciate the genre, you can appreciate that it's a fantastically constructed piece of music. I'm not a big rap fan, but MF Doom, Madvillain, Big Boi and Andre 3000 are making brilliant music that's doing something for the genre. Drake, Akon, 50 Cent, for example, are NOT. They're writing shit generic music that's doing nothing new and nothing interesting or original.
The same's true for metal. Trivium, Bullet for my Valentine, and Avenged Sevenfold, among others, are writing music for money, and doing nothing that hasn't already been mastered by the creators of the genre. (A7X at one point were writing interesting music but they've forsaken that now). At the same time, you have pioneer's like Protest the Hero, Between The Buried and Me, Coheed & Cambria and Cancer Bats doing things that have their own unique sounds, without hugging the genre too closely, and at the same time, a mastery of their instruments. You won't find a drummer on that level outside of Coheed, some of Cancer Bat's dischordant riffs are completely unique, and BTBAM... well. Give Swim to the Moon a listen and you'd understand.