I find his books to be a bit too light on the content. All of them combined would've made a great book that would still be of a reasonable thickness, but he is self-published and he makes his living from lectures and book sales, so he's probably not too interested in that.
Tufte has some great ideas, but would benefit from a ruthless editor. As a guy who's self-published, he does not get the benefit of that kind of feedback.
If you just want to make better charts, buy, a from memory guess, Envisioning Information. It provides most of the basics of The Visual Display of Quantitative Information but develops the ideas a little further and provides better, more modern examples. If you think it's a cool topic then buy them all because they're all pretty nice books.