I've only just started reading this book, so can't yet comment on whether it's good or not. However, in regards to your comments about "raves on about the turgid and almost-unwatchable CREATURE FROM THE BLACK LAGOON as if it were a masterpiece", isn't the selection of films King chooses, a personal issue?
Therefore, there's no right or wrong anwer to it.
Some people love CREATURE FROM THE BLACK LAGOON, and some hate it. Some think CITIZEN KANE is the best movie ever, and hate THE GODFATHER. I rate CANNIBAL HOLOCAUST as the greatest piece of horror cinema, but feel that THE EXORCIST is merely good. Does that make my choices any more or less valid than Kings, or yours, or anyone elses? And should it really matter whether his choices are in direct agreement with yours, anyway?
No book can ever cover the entire genre of horror, across film, TV, literature, comic books etc, and King mentions this in his introduction. (At least in the 2012 Introduction in the new Paperback edition, he does.) He also states that no one author could ever attempt to cover such a subject, in one book, and he states that DANSE MACABRE is just his view of the subject. It's personal. It's not definitive, and thus should not be used as a history or overview on the subject. It's more of a book containing his opinion on various themes.
And if that is the case, then how can you, or I, or anyone else quibble with it?!
This isn't meant to be a hardbook reference tome on the history of horror literature, or horror films, and doesn't try too. So your complaint seems to be about something, that you believe the book is not actually attempting to be, in the first place.
It is, as you say just "his opinion". And to be fair to King, a lot of "trashy" horror films can still be great fun, even if they may not be worthy of being labelled as "critically-acclaimed" works. (And who or what defines "trash" anyway?) Very much like King's own novels, in fact - which are hardly in the same vein as the likes of Dickens, Dostoyevsky, or Joyce - but again, don't attempt to be either. Or are you saying his works (such as CARRIE, THE STAND, CHRISTINE or THE DEAD ZONE) should now be being compared with the likes of DOCTOR ZHIVAGO, GONE WITH THE WIND and/or A SUITABLE BOY?
And should we consider GONE WITH THE WIND to be more or less worthy than CARRIE? Can't both survive, on their own, and be accepted for the sum of their parts, rather than being compared to each other, and readers being forced to decide which one is more "worthy" of existance?
Literature, like horror films, are something just to be enjoyed.