A few thoughts: I've seen this referred to as one of the best non-Dracula, non-Frankenstein Hammer films, but I honestly wasn't very impressed. It felt like a very standard Dracula movie set-up, just with a considerable lack of Lee's daunting presence. There were aspects I enjoyed about it, particularly the elderly man who helps out the main protagonists in the third act, as well as the entire third act as a whole involving bats and a cult of vampires, but the journey there was fairly standard. As is always the case with Hammer horror, the sets, costumes, and lighting were pretty great, but it was the story that didn't really grab ahold of me. All-in-all, I definitely wouldn't consider this a bad movie, but of the 2 dozen (or so) Hammer films I've seen, this is among the weakest as far as I'm concerned. One of the only highlights is, again, watching a ton of bats fly around attacking people in one of the final scenes of the movie. That was at least entertaining. As a film overall, it's not good, not bad, mostly just bland and forgettable.
Who would I recommend it to? Only the most dedicated fans of Hammer horror, as it's a fairly standard effort from the studio. Would definitely recommend starting with the Dracula series if you're interested in their vampire movies, though.