If you loved Frankenstein Must Be Destroyed, try Frankenstein and the Monster from Hell
A bridge between a film you've already seen and one most people haven't. Here's what they share, and what the second one does that the first one doesn't.

Frankenstein Must Be Destroyed

Frankenstein and the Monster from Hell
What they share
Both films are directed by Terence Fisher, and they both carry the body horror, dread mood tags, and they sit in Horror / Science Fiction territory. If that's the register that drew you to Frankenstein Must Be Destroyed, the second film will land in a comparable space — through a different lens.
What Frankenstein and the Monster from Hell is
The asylum’s padded walls hush a wet March. A scalpel scrapes bone. A disgraced surgeon meets the asylum’s director, an exile from old experiments. Under flickering bulbs they stitch a corpse from stolen parts, choosing the screaming as fresh flesh. Fisher conjures gothic dread in 74′ British horror.