This is probably the best critical overview of nightmare movies (primarily horror but use of the word 'nightmare' takes it down some unexpected byways) that you're likely to read. It's so extensive that dozens, if not hundreds, of titles get a scant half dozen words about them and as often as not just a mention of the title in a broader look at a subgenre. For major works. however, there may be a couple of thousand words.
If you haven't come across Kim Newman before, he is one of the leading experts on horror movies in the world, not to mention SF, fantasy, and possessing an enviable knowledge of cinema in general. He's also highly knowledgeable in the literary genres of horror, SF, and fantasy, not to mention being an eminent practitioner of them himself. Basically you can't go wrong with any book by this author.
Here he is at his wittiest, most insightful best with half a new book. The first half is basically the previous edition with new (extensive) footnotes in which Newman provides extra information or admits he's changed his mind, and other goodies. As it's thirteen years since it was originally published, Newman has a whole lot more movies to consider but the tone of the second is surprisingly consistent with the first.
If you have a relaxed definition of what constitutes a horror movie, you'll love this book even when you're disagreeing with the author. I did find it sometimes frustrating when he skips casually over movies I've particularly enjoyed but then this is a survey not an encyclopaedia so it would be unfair of me to criticise the book for being something it wasn't intended to be in the first place.
Highly readable and highly recommended.