Surprised noone has mentioned this yet, but here's why I'm not a fan: He didn't teach creativity, he taught techniques. Anyone who watched him enough could follow the techniques to create a painting with mountains, trees, bushes, etc. But in the end, you are left with nothing original or inspiring.

To compare with programming: Bob Ross did the equivalent of teaching non-programmers how to copy-and-paste specific snippets of code. It's enough to patch together a sloppy program--which may or may not work--with the snippets you're taught, but it doesn't give the ability to solve problems with code.