A bit iffy. There's a lot to enjoy here, but it's quite a hodge-podge. I can't believe there are people who find this better than House of Dracula.
The most obvious problem is the script. At one point this was going to be a mish-mash of even more monsters, including the Mummy, the Mad Ghoul and perhaps the Invisible Man. Even this film's fans admit that it feels like an anthology rather than one coherent story. It starts with the the evil Dr Niemann (Boris Karloff) and his faithful hunchback Daniel (J. Carrol Naish) escaping from fifteen years' captivity. Whoever put him there had the right idea. Niemann is a Frankenstein fan and hopes to recreate the great man's experiments, but before that he'll faff around for twenty minutes resurrecting Dracula. Why? Good question. Eventually he finds Frankenstein's Monster and the Wolfman, frozen together in ice after the ending of their last film together, Frankenstein Meets the Wolf Man (1943). There are also gypsies.
Did I mention the hunchback? There's always a hunchback.
The main story stops dead when Dracula shows up, then returns twenty minutes later once he's defeated. This film's subplots sprawl all over the place without coming together. There's a love triangle involving the hunchback, the Wolfman and a gypsy. There's Niemann following in the footsteps of Frankenstein. There's the Monster itself, used almost as sparsely as he was in House of Dracula.
Still less forgivable are the fates of these classic icons. Of course they're all destroyed. Naturally. They're monsters. That's their job. All we ask is that their demises be satisfying, but somehow not a single one of those three farewells manages to impress. Dracula and Frankenstein's Monster both meet their fates through dumb luck and/or stupidity. That's not so terrible in the case of the Monster since it's not noted for brains, but the world's most convenient sunrise makes Dracula look like a twonk. Then there's the Wolfman's downfall, which could have been great if it hadn't been for the Hays Code. These classic Universal horror films couldn't show us anything juicy, especially when it came to violent murder. (Well, post-1934, anyway.) Normally this doesn't matter. You can do it with shadows, silhouettes, last-minute pans and the like. It's atmospheric. It's the style of the films of that era and one simply accepts it. However this killing happens to be dramatically important and being unable to show it hamstrings the film.
It's incoherent. It's fine as a string of set-pieces and disjointed plot threads, but it doesn't fly as a complete dramatic work.
The cast was oddly disappointing too. Carradine's doing exactly what he'd do again in House of Dracula, which is to rest his performance almost entirely on his aristocratic looks. He still doesn't convince me as a vampire. He can turn up the heat to some extent when facing a victim, but his Dracula is a laid-back, unflappable gentleman. It's a performance without weight.
Lon Chaney Jr is... well, Lon Chaney Jr. He knows what he's doing with the Wolfman and he does it. No problems there. Then there's Glenn Strange, making his first appearance as the Monster. Apparently Boris Karloff coached him, but he's basically a stuntman in a mask. He does everything the script requires of him, which isn't much.
No, Boris Karloff was the real let-down. What's interesting is that he's basically playing Peter Cushing's Frankenstein from the Hammer films. At this point those were only a decade away, incidentally. This is no well-meaning but unlucky scientist, but instead a murderer who'll betray his friends without a second thought for the sake of his experiments. They even have the same accent! Unfortunately Cushing's Frankenstein would have eaten Karloff's Niemann for breakfast. Karloff was a big man and a remarkable physical performer. He had amazing eyes and could turn on the malevolence with the best of them, but sometimes here he's oddly undercooked. Give him juicy material and he'll play it to the hilt. There's still plenty of classic Karloff to enjoy here, but he can also fade into the background a little in filler scenes where his story isn't really going anywhere.
It's clear that like Carradine he wasn't a Method actor. This film gave me the impression of a brilliant performer with a rich bag of tricks, rather than a complete performance. Personally I think he was a better and more versatile actor than Cushing, but in this comparison he comes off worse.
The more you study this film, the more you realise that it's less than the sum of its parts. It's certainly enjoyable, but it helps to screen out the shoddiness and concentrate on the good stuff. In fairness though, those good parts are very good indeed. As with House of Dracula, it might surprise you by taking seriously a premise that might seem more appropriate to a Saturday morning children's show. This is a proper film (albeit very much of its era) that shouldn't need to be making excuses to anyone.