This is a typical "old house" film.....a black-clad figure that throws gigantic shadows on the walls, a secret entrance, all the characters "creeping around", a creepy butler, and all the rest!
It's interesting that they use some of the same sets for that other fantastic "old house" film, Dr. X. (Most notably, the upstairs hall & the kitchen).
Some people would say this film is "slow moving", but that is done deliberately to increase the creepy "something-is-about- to-happen" feeling.
As an aside, it's remarkable that the actress who plays the sick old lady looks really OLD in this film, but in Bob Hope's "Cat & the Canary" (filmed almost 10 years later, as the Aunt) looks MUCH younger! She had one heck of a make-up job in THIS film!
If you love "old house" films, don't miss it!