I'm a fan of the Head First series. They make a welcome change to the staid text book style of the majority of computing books. However I think this particular offering is not one of their better efforts. Maybe Ajax isn't really that complex a topic and doesn't require a book of this length, or maybe the author spent too much time on the Head First fun filled packaging and not enough on the content. I actually found that the Head First fun and frivolity actually seemed to pad out the book and unnecessarily labour what is actually a fairly straightforward topic.
In the end I got bored with the book and sold it on ebay. The other Head First books I have bought are outstanding. Head First Java (Head First)
, for example, does an excellent job of making difficult topics intelligible. The problem with this book is that all the dumbed down explanations make you feel that Ajax is a more complex topic than it really is.