However, I am not necesarilly a purist about these things. Because I can still enjoy it on its own if I haven't seen the original first, and that's why I'd recommend Nightmare Castle to any fan of B movies, Italian Gothic horror, Bava-esque settings, and of course...Barbara Steele. The one and only.
Throughout this film, I found myself mostly appreciating the set...the house...the costumes...and the fact that it really wasn't as slow as some people would have you believe. Especially if you're used to the sort of dragging elements Italian cinema is especially known for, the general classic philosophy of their filmmaking being that 'cinema is about the art and the experience, not the plot or the philosophy of being concise.' Taking that into consideration, there's quite a bit of plot in this that you wouldn't otherwise expect. A mad scientist tortures his adulterous wife to death, uses her blood to youthen their maid (who is obviously his dish on the side), then marries her step (or half) sister to get the family property and fortune...did I mention Barbara Steele is in dual roles? Barbara Steele is in dual roles.
A great film for the approaching holiday season. Check it out as soon as possible, and especially if it's dark and stormy in your neck of the woods. You won't regret it.