I've been on a great Hammer (British 1950s-60s Horror Films) kick, watching the late, great Peter Cushing in almost all of them.
Cushing films are always entertaining to watch, no matter how horrible the overall plot is; because Peter always put 500% effort into his acting. He knew he was chewing the scenery; but he did it with such seriousness that you could believe in it; following the well known maxim of:
"This may be a completely ridiculous concept, but we're gonna take it seriously to make you believe it's real."
However, there's a good rule of thumb for almost all Hammer Franchises like Mummy + Dracula + Frankenstein:
The first movie and it's immediate sequel are decent; while every successive film afterwards becomes worse and worse, to the point that even a great Peter Cushing or Christopher Lee performance can't salvage the film.
In the case of Hammer's Frankenstein; the first two films are great and form a self-contained cycle; but the third completely loses the plot.
Wikipedia (https://en.wikipedia.org/wiki/Hammer_Film_Productions) helped me understand what happened with Hammer Frankenstein:
The first two films were produced under previous agreements with Universal Studios (so as to avoid messy and expensive copyright fights) which limited what Hammer could do with the story of Frankenstein.
Thus, in the first two Hammer films, Baron Frankenstein is the true monster, not whatever he's created and 'expensive' sequences considered 'core' to the Frankenstein story such as:
* Using a lightning storm to bring the monster to life.
* Villagers forming a mob and destroying Castle Frankenstein.
were deleted for budgetary reasons and copyright reasons, forming a unique "Hammer Frankenstein" that worked because it was fresh and different.
For the third film, they negotiated a new agreement with Universal, allowing Hammer to more closely follow Universal's films; and as a result, the third film (and all subsequent Hammer Frankensteins), per Wikipedia:
Does the above passage remind you of anything?"Each subsequent movie in the series contains elements that do not relate to (or flatly contradict) the events of the movie(s) that went before, whilst the characteristics of Cushing's Baron [Frankenstein] vary wildly from film to film, resulting in a series that does not progress as a self-contained narrative cycle."