This starts out as a fascinating analysis of what was good and what was bad in the scripts and production of the series, seen from the point of view of a script editor in the final years of classic Who (the McCoy years). Rather than being a fan appreciation, Cartmel gives a technical insight into what makes a good story, and why good stories can be wrecked by bad props or casting the wrong actor (e.g. Davidson as Who). He also suggests where even fan favourites are weak because of factors which fans might choose to ignore. I mostly agreed with his conclusions from the Hartnell years right up to the point where he became the script editor himself, and then it was time to be self-critical.
Sadly, Cartmel lacked the ability to recognise flaws his own era, and praises stories which all my friends regard as complete turkeys (complete with stuffing and roast potatoes...). He isn't completely blind to faults in Curse of Fenric, but praises Rememberance of the Daleks for all the things which he criticises in earlier stories.
This is a very good book for the parts of Whostory which Cartmel isn't personally responsible - it's always easier to criticise somebody else's failings - but he is not a reliable judge of his own. So read the first chapters, and don't bother with the last ones, and you'll find this a fascinating read. I finished it in a day, and it is arranged in bite-sized chunks to make this easy, but leave it to others to do unto his work as he did unto others.