The book is very concise and probably one of the books with higher ratio of relevant content per page. It also teaches you the grammar of JavaScript in one of the most simple and unambiguous ways I ever seen in a book (railroad diagrams).

On the other hand it was one of the shortest book I ever read in which I had to reread and go back more times. JavaScript can be a bit confusing at times and the book only says things once and in a succinct way.

Everything was going fine until Prototypes and Constructors and the very bad 'new' operator, that somewhat surprisingly was used in the good function which achieved Prototype Inheritance (example in here: http://javascript.crockford.com/prototypal.html), but after a while I got it. ;)

It's the only book I've read about JavaScript yet. I consider it very good if you already are proficient in other programming languages, but it doesn't really show you what to do with it (and it wasn't supposed to), so I'm now planing to buy JavaScript the Definitive Guide.