For the past year or so I have been puttering with R, but never really "got it". This book is just what I've been looking for, to understand what R is "thinking". It isn't a cookbook with loads of examples, but a thorough guide to understanding how R works and how to be productive in it. After only an hour, I understand data.frames, and the environment structure better than several nights of struggling with the online documentation. This isn't really a book about how to analyze data, it's about becoming comfortable and expert in R to make it easy to analyze data. Once you understand the tool, the data analysis becomes much much easier.
I agree with the reviewers who say it's chatty, but that makes it very readable. You don't have to work every example to understand the points the book is making. Likewise, it _is_ cross referenced to death, but it's easy enough to read over the links, and when you're trying to make sense of something, the cross references do take you to the right information to round out a picture.