Freakonomics is a great book because it introduces fundamental principles of economics on intuitive grounds. So you're not talking about incentives with respect to society or some other abstract entity, but with respect to specific cases. Plus, as I mentioned above, it's an extremely fun read. Very well written and the ideas presented are definitely compelling. I'd recommend to go as far as to read the original research papers that the book is based on. Especially the abortion-crime one.