This is the best single volume book on the subject of information visualisation that I've read. Sure, there are other very nice books on diagrams, maps, data analysis, modelling and scientific visualisation. However, none of them have the scope of this book.
And therein lies the problem. For a single volume book Ware's effort tries to cover too much and some of the chapters are quite weak (chapter 0 and 10). Also, the fact that it was written by a psychologist shows in a good and bad way: human visual cognition is correctly the foundation upon which to build visualisation. Unfortunately the examples and the ideas for implementation are often lacking or poor in quality.
The first edition also has typesetting errors, so be sure to get the second edition.
All in all, it's still a book worth getting if you're in any serious way connected with the practise of visualisation. However, don't expect it to be the bible of the field, as such a thing does not exist (yet).