I'm a bit more mixed. I found his presentation style pretty terrible and his specific contributions (viz and software) not terribly exciting. But he's a master at analyzing other people's visualization work with an almost mind-altering critical eye. His books are incredibly valuable.

I think it's probably just worth it to buy the books and read them, but I did find his walkthrough of a few visualizations enlightening.

I still recommend the class, but with the caveats mentioned above.