This is definitely one of the lesser Hammer movies. Whilst the director has been creative with the obviously tight budget, my biggest problem is the dull script and the awful miscasting of Anton Diffring. Diffring always made a reliable supporting actor but I feel he really struggles to carry this film. The dialogue is also terrible at times and whilst Peter Cushing was a master at delivering terribly written dialogue due to his excellent natural delivery and magnetic presence, Diffring just doesn't have the same ability. Don't get me wrong, Anton Diffring was not a bad actor, he just doesn't seem comfortable here that's all. I know Cushing wasn't available for filming yet Herbert Lom would have been a better fit as, like Cushing, he too had a style of delivery that transcends bad writing and would have papered over the cracks.
That said, the film is a middling Hammer effort that is part Baron Frankenstein and part Dr Jeckyl and Mr Hyde. It is also an early Hammer effort, so the studio had not yet perfected its style and consistency yet. With this in mind its faults can be mostly forgiven as the visual is already there. So all in all this is a flawed film that is worth a watch but lacks the punch and panache of classic Hammer and shows how getting the casting right is so important.
That said, the film is a middling Hammer effort that is part Baron Frankenstein and part Dr Jeckyl and Mr Hyde. It is also an early Hammer effort, so the studio had not yet perfected its style and consistency yet. With this in mind its faults can be mostly forgiven as the visual is already there. So all in all this is a flawed film that is worth a watch but lacks the punch and panache of classic Hammer and shows how getting the casting right is so important.