Karloff, as always, is a delight, and to see him in another movie with Ernest Thesiger is a bonus. Also, The Ghoul expertly incorporates a bit of Richard Wagner's "Der Götterdämmerung" into its soundtrack. (Previously, I'd been associating that music with Excalibur (dir. John Boorman), but I think I dig it a LOT as a funeral march now!)
This is the lanky, younger Karloff, so he's this thin creep of a man in the movie, and his performance (combined with the make-up) gives him the look of a professor-turned-ghoul. He exacts his revenge on those who've wrong him . . . and it's unnerving. I'm purposefully being vague about many more details of the movie because it really is something I think more people should see for themselves!