I was pleasantly surprised by how good this was. I'm sure it helped a lot that Christopher Lee was the eponymous character - I thought they were going to pull the old switcheroo after the opening scene, but Lee actually remains in the movie.
The plot here is paper thin, so don't expect too much there. This is simply a spooky, gothic horror movie. The lighting, sets, fog, costumes, and general atmosphere are the real stars. Also, doesn't hurt that Karin Dor looks like Barbara Steele's little sister. Perfect film for a dark and stormy October night.
As for the plot itself, it's weird, even by '60s horror standards: It's somewhere between a ghost story, and a vampire movie. Our Count is using science or magic or a mix of both to return from the dead. Reminded me a lot of _Re-Animator_, but this is supposed to be based on Poe - aside from the Pit and the Pendulum moment, I can't say... I seriously need to brush up on my E.A. Poe.
The only major flaw here is some of the music: there is a song that is so out of place, it sounds like it belongs in a goofy comedy.
Overall, very good. I say this is a must watch for fans of classic Hammer-era horror.

Post script: This movie has several guest spots from our creepy animal friends: snakes, tarantulas, vultures, rats, scorpions. Thankfully they are left alone for the most part. However, a snake is thrown at one point; there is a cut, so it's difficult to tell what happened to him, but there's no visible damage, from what I could see. Thankfully this was not made in Italy. Animals are here with us, not for us.