I've always been a bit wary of this film, knowing that it is viewed as a pleasant oddity, but... well, the concept is so silly, as was the marketing of the time, it just couldn't work. Now could it?
It not only could, but it actually does. This film has some great moments that are very cleverly done. The first transformation of Jeckyll into Hyde is well done, as are Hyde's erotic conquests of Jeckyll's male acquaintances (and one particular unnerving moment when during her lovemaking Hyde regresses into Jeckyll!).
There is some comedy as well, but I was surprised at the raw violence in the film. It's never fun and games, the tragedy of the original tale is ever present.
The only qualm I have is that the film loses its focus near the end. Why Jeckyll murders prostitutes is easily explained, but what's in it for sister Hyde when she takes to the task? It appears Jeckyll and Hyde are conscious of one another's conflicting desires, but Jeckyll is also able to use Hyde to execute his design's under another cover. The conclusion, although tense, doesn't satisfy.
But all in all a real horror oddity that epicures in the terrible should not dismiss.