This truly is, as the subtitle says, a Practical Introduction. Kieran Healy writes about data visualization in R with a wonderful style, as if he is at your side teaching you (he is a Professor of Sociology).
Data Visualization is an emerging topic. What the title and subtitle are missing are the fact that this books relies heavily in the R programming language. So it was a bit hard to learn about data organization and visualization, at the same time that I had to understand R notation.
The book organization could use a bit rethinking. The Appendix, for instance, is very important and should be moved to an introduction - I can't undestand why the author waits for the end to explain why the plots you produce by following along the examples in the book do not match the plots in the book.
If you decide to learn R and data visualization, keep in mind that you have to look up a lot of details missing in the book. But this is also a good learning experience; in real life, data is badly documented.