It's hard to rate the book properly, as it's not usual one. It is concise and easy to read as if it was a post in the blog - you could get a quick impression about technology advertised. Similarly, it requires some care from the reader's side to exactly reproduce certain aspects of the examples, while the attitude towards a tool is in 'vulnerable' state.
Gotchas:
- Stuff from the books might fail to work for you due to versions difference(1.2 failed, 1.1.2 worked for me)
- Play! framework lives in the highly competitive world :)
- Integration matters