"Suggested by the immortal Edgar Allan Poe classic", which is one of the film's main drawing points, the other being the pairing of this natty bro:
And this limey cocksucker:
The Black Cat bears little resemblance to what Poe wrote, so it's best to view it as an entirely new work rather than an adaptation. Lugosi is Dr. Vitus Werdegast, a noted psychologist, who has a history with Hjalmar Poelzig (Karloff) dating back to their time at Kurgaal Prison. Werdegast was a prisoner there, Poelzig ran the place. Along for the ride is a mystery writer and his flapper wife. The ride ends with a car crash near the house of Poelzig and the ensuing movie is built around the eventual confrontation between Werdegast and the ex-jail supervisor.
Okay, PS, Poelzig is holding Werdegast's daughter in the house as his wife-prisoner of sorts and, also PS, he is a practicing Satanist who is getting ready for the next big Satanic holiday. This is not a good movie if careful plotting is essential for you. The story gets knocked down the to-down list in favor of atmosphere, lumbering camerawork, and Lugosi-Karloff resentment.
I dunno if you could call the resulting whole a "good movie" in the scientific sense, but it's certainly packed with cool stuff. Lugosi gets to speak in Hungarian and deliver lines like "A masterpiece of construction built upon the ruins of a masterpiece of destruction - a masterpiece of murder!" Karloff gets to have a triangular haircut and deliver lines "Even the phone is dead!" Apparently dead people float in vacuum tubes while their clones are alive and kicking elsewhere(???). We are all having a blessed day today.
As with From Dusk Till Dawn, you could cite plot as this film's weakest element. But with that film, the plot problem was mostly excess smugness and fumbling construction. In this movie, what we get is pretty much incomprehensible, the kind of tangle that only a fool would try to penetrate. On the upside, the horror elements that you love are pretty much here in full force and, at barely over an hour, there's not enough of The Black Cat to make you regret your investment.