This sounds as if it's going to be great: Boris Karloff is executed for a crime he didn't commit, is revived from the dead and sets about getting revenge on the people responsible for framing him. Throw in Michael Curtiz as director, the great title, the Frankenstein trope, and Edmund Gwenn and Ricardo Cortez in the support cast and I'm thinking "how come this isn't better known?"
The answer: because it's not very good - more specifically, it whimps out. It gets off to a confusing start, with someone other than Karloff sentenced to jail, then Karloff coming along having been sentenced to jail, then getting accused of the crime he didn't commit. He gets executed because our romantic lead couple are too scared to testify until the last minute, which makes them extremely unsympathetic. Doctor Edmund Gwenn isn't a mad scientist, he's conscientious and doing his bit for Good, which is disappointing (if only they'd cast Bela Lugosi! Or written Gwenn as a Lugosi type!)
Then, most crushingly of all, Karloff doesn't actually kill the people responsible for him winding up dead, he just sort of is responsible for them dying but invoking their guilt - and it's their guilt that kills them. Zzzzzzzz. I assume this is for censorship but it results in a horror film with no balls.