I've read several books on and around screenwriting, but this is the only one that manages to be instructive and educational, without being laboured or preachy. Although it is (understandably) focused on Hollywood, there's a special foreword (and wider scope) for British readers which makes a refreshing change - too often these sort of books are pitched at a purely American audience. Michael Hauge writes honestly and with pace, and there is a levity to the book that makes it more friendly and readable than others that are more lecture-style. Rules are only laboured consciously; the important facts are reiterated throughout the book to ensure they are not forgotten, not out of lazy editing. Everything you need to know is packed into a concise guide that leads basic structure, characterisation and plot development into the more technical areas of motivation and themes. It's easy to get into and unputdownable once you are. However, I'm not too sure about his case study script - "The Karate Kid" - but that's just personal preference.
As an introduction or a supplemental guide to screenwriting, this is unmissable. Inspiring, informative and very enjoyable.