he seems to be the type who can cover a lot of styles
i don't see what's wrong, in fact his cartoon images seem to fit perfectly for those old age powerpoint things i forget what they're called
You don't have one of his "How to Draw Manga" books, do you? What he calls manga is a really inaccurate, Americanized version of it that looks completely illogical and stupid. I'm fine with his cartooning style, but his "manga" style has absolutely no excuse, especially because he acts like an expert on Japanese culture, but he's clearly ignorant.
I took some pictures with my phone of the lesser quality pictures he drew (most of his books are collaborative works. It's usually obvious which pictures are his). I honestly would have no problem with him if he weren't so arrogant about his art on dA (he tends to delete comments with negative constructive criticism) or if he didn't make tutorials. Anyway:

The fact that he calls these drawings "manga" is really annoying. Having spiky hair and googly eyes are not the only characteristics of any Japanese cartoon. The physics in his hair, even in his better pictures, are really abstract, too. Even if it is stylistic, hair doesn't just float on one's head, nor does it curve the way the red-headed girl's does. Oh, and if those pictures don't prove my point, I should probably share the page my avatar is from (this picture was not taken by me).
If you're going to use these pictures to explain how to convey different emotions to beginner artists, I'd be very concerned. And, clearly, I am.