I have not seen it since I was a kid, and at the time I thought "whatever, it is no Last House on the Left." But when you see it as an adult you realize how cool it is.
First of all, it is definitely a Dracula for the Ladies, and in that sense it sort of reminds me of the Twilight series. Also, the production design and the score by John Williams are really over the top and absolutely wonderful. The film really has a creepy, Gothic vibe to it, which you would not expect for a film from the late 70's.
Plus, Donald Pleasence plays Dr. Seward. He is one of my favorite actors (he is Dr. Loomis after all.) In the extras feature Frank Langella talks about how he was warned that Pleasence was a "hanky" actor. Meaning that whatever scene he is in he will be doing something to focus attention on himself, whether that means playing with a hanky or eating candy, in order to get more screen time. And it is true. Throughout the whole film he is eating candy, so even when he is in the background you kind of focus in on him. Now I have to re-watch Halloween just to watch him scene stealing.