I've seen this film a few times now and it wouldn't be my favourite Hammer - I admit to being more frightened by Dracula - Prince of Darkness. But it works beautifully - Christopher Lee deservedly became a star with his count, all virility and action; he was a mediocre Frankenstein's monster, but a beautiful Dracula. And has there ever been a better Van Helsing than Peter Cushing - brilliant, whip smart, tough, imposing.
The music and art direction are first rate; Jimmy Sangster's script is a expert example in low budget adaptation. The limited budget helps - it adds to the feeling of isolation and spookiness. And there is a pleasing sexual frankness to it all: clearly the women can't wait to get a decent ravaging from Dracula, especially Melissa Stribling.
In the support cast, Michael Gough and John Van Eyssen are particularly drippy as the supporting men - respectively a disbelieving idiot (and clearly a lousy lay) and not particularly effective assassin. The women aren't as attractive as you'd get later on, but the acting is pretty good. Spectacular finale.