Tufte's book includes a range of beautiful examples of information visualisation, but also wanders off in places in a slightly self-indulgent way, and uses a lot of space to cover some of the examples (Tufte self-published the book, I believe, which might explain this).
In the same way as "The Design of Everyday Things" causes you to look at door handles in a new light, you never look at a chart or diagram in quite the same way after reading one of Tufte's books; bad design will leap out at you once you've seen examples of good design.
He also includes the obligatory powerpoint-bashing, but in good humour.