It's almost not worth saying anything at this point, since this movie is set to expire soon. When it comes to film history, I can't help myself (If they showed more Hammer films I would be typing all the time). American International Pictures was the spring board for the great Roger Corman who gave many of todays top film makers their first break. This film is considered one of the "Corman Poe Cycle" and although they had little to do with the writings of Poe (more so that it exploits the author who's works were in public domain), they did introduce a new generation to the author.
Before the mid to late 1970's (When AIP went legitimate) they made nothing but exploitation films. First with teenage exploitation films (Which set the pace for films like Friday the 13th) and then with Black exploitation films like "Blackula".
This film gave work to three actors who couldn't get work in Hollywood at the time, Price, Lorre and Karloff. This film also used the matting process pioneered by Hammer films in London at the time (Look at the castle shots-they are paintings, not real duh !) and AIP also used film painting to make the "ectoplasm" extend from Price and Karloff's hands, this process is far outdated today, but was state of the art at the time.
Horror films had great success in film during the 1930's, but was turned into a comedy format in the 1940's. With the birth of low budget films through independent low budget exploitation film companies like AIP and Hammer the genre was given new life and is the foundation of modern horror films.