(this review was posted in Amazon)
The author tells you why HTML5 took for ever to come out. Then, it starts from the simple elements that now have a shorter syntax and new semantic elements that are intended to specify that a web page has articles, sections, header and footer. It always tell you why something exists, which is very helpful as compared to just providing examples with their respective screen shots as other books do or as you would get from finding the examples yourself searching online.
The book will not disappoint you but the support of HTML5 may do so, depending on what you want to really do. For example, it seems too much work to get different versions of a video in order to make it work in most web browsers. It is not a problem of HTML5, it is a problem of lack of agreement among Web browsers and of patents behind (most of) video codecs. The new elements for forms are the best example of lack of browser support on elements that, after a decade, you would imagine would be standard components by now. The microdata elements, actually, attributes instead of elements, show that also after a decade of “Semantic Web”, the semantic markup of content of web pages will likely be based on a practical solution that is easy to implement for the html/web developer, as opposed to other methods that never really took off (such as microformats and RDFa).
The things that seem promising in HTML5 are the canvas, storage for web applications, and geolocation but it will depend on whether you will really need to use it or not. If any of canvas, storage, geolocation or video interests you, and you are new to using them in HTML, then this book is way better way to get it right as opposed to finding examples online.
Disclaimer: I received the e-book HTML5: Up and Running (valid for 30 days) from O’Reilly. I needed to know about the “video” tags anyways because I will be using them in deploying a website with a few hundred of videos soon.