Rating: 

It's style is definitely terse, and requires a close reading - but that's a strength, in my opinion. Every sentence matters. One benefit of that style - and the consequent brevity of the book - is that if you find yourself confused about a topic, you can easily go back to the relevant section and review it; not as easily accomplished in a more verbose text.

The chapter dealing with associations was particularly of insight to me - illuminating how models can be tied together so that their sum is greater than the parts. Also, the little rake task that they provide early on is a beauty and helps clear up the inevitable migration issues.

In summary, it's a very concise, 'meaty' introduction to RoR.
Good job!