I found his class very ho-hum -- it's mostly Tufte quietly rambling over a number of examples and promoting some of his ideas (artistic and otherwise).
I went with a small group and many had never heard of Tufte before. They were so turned off by the class that they swore him off before it was over.
Later, many of them came around after they read one of his books, which are excellent and his work has slowly become very influential with my group.
I think what Tufte does very well, is to bring a well reasoned critical eye to deconstructing other people's information displays. I don't think he's as good at synthesizing information displays -- his major work being the sparkline and his books. As a result he can come across as dismissive of other people's hard work.
The people who got the most out of his class seemed to be those that were already quite familiar with his method of critical review. I don't think I would bring people to his class who weren't already quite familiar with his methods.