I cannot rate this book highly enough. Every Shakespeare play is outlined Act by Act, Scene by Scene in a concise, easy-to-understand format that means I now cannot watch a Shakespeare play without this and a good version of the text in front of me. For that alone, this book is well worth buying.
There is a lot of other information in here, but - by its very nature - it does not go into as much detail as other studies. However, as it is co-edited by Stanley Wells, one of the leading contemporary Shakespeare scholars, it's all of a very high standard.
I'm sure I paid more for my copy than the current price (as of Jan 2010) - it now seems an absolute bargain. It is a big book, but then, it is on Shakespeare.
If you're studying Shakespeare's plays academically, or just for pleasure, this book is absolutely essential if you want to understand every line.