It's a B-horror film that's a touch hard to pin down because the threat doesn't follow the usual horror conventions. Are they vampires? Are they zombies? Why is there is a group of people meeting on the beach staring out into the sea at evening? Why are the streets of the town empty at night? Nobody is turned by a bite or anything else like that. Even as their origin is revealed it's still somewhat unclear but in the "we don't need to explain every small detail in a pedantic way" style.
This movie originally was marketed in some places as "Return of the Living Dead" believe it or not, with poster work stolen directly from the original NOTLD and taglines and review quotes from Dawn of the Dead. Some distributor thought it would be a good idea....