The vampires drink blood to survive but besides this they seem pretty human. They can tolerate daylight, but not direct sunlight. They also are not all that powerful, but the head vampire can summon one of his brood from afar, and no mention is ever made of immortality.
I liked everything in the movie until a scene where where the vampires are sent into turmoil by the hero making a sloppy sign of the cross on his chest in blood. The idea of the scene is fine, but a better looking cross would have been much more believable. Besides that, the movie creates a great mood and very watchable, fast-paced story. There is almost no downtime or slow or boring scenes. The Van Helsing like character of Professor Zimmer is unique in that he is a weirdo, reclusive drunk, instead of the dashing and able know-it-all Van Helsing.
The picture is decent enough in a 1.66:1 transfer, considering it is not anamorphic, but there were many scenes with an over saturation of red. The sound had many pops and crackles and the disk has only scene access on the menu. There are no extras at all, not even a trailer. Disk shortcomings aside, the movie surprised me with how effective it was and how watchable it was 39 years after release. If you can get the movie for under $15, I would definitely consider adding it to your collection.