Photoshop is an immense programme, and one about which numerous books have been published. So far I have yet to come across I book I consider to be the definitive guide, but this one certainly demystifies the use of Layers, which is the aspect of Photoshop that stands it apart from other photo-editing software. On the whole, there are very clear explanations of how to achieve specific effects, ranging from very simple to quite complex. Like any book on a huge topic, the coverage is not exhaustive and some chapters are better than others, but there are certainly hours of entertainment to be had from working through it.
There are two reasons why I did not give it five stars. The first one, which at least one of the other reviews here highlights, is that not everything described in the text correlates precisely with what appears on the screen, and there were a couple of times I just could not get the programme to do what the book seemed to intend it to. The second point, and this may be related, is that you are supposed to be able to download the pictures used in the book from the Kelby publishing website, so that you can work through the examples. I found that the downloads were simply not there when you try to access them, which means that you need to work with your own photos and are therefore never quite sure if you have followed the instructions perfectly. I have found the absent downloads to be a feature of some of the other Kelby publishing books I have purchased, such as the HDR Book by Rafael Concepcion, so I suspect they are only available for a limited period following publication.
Consequently it is not perfect, but it is pretty good.