A few thoughts: Incorrectly billed as a horror movie, Night Creatures (or Captain Clegg) is a pirate/smuggler adventure thriller with some strange inconsistencies and unclear motivation. Who is the hero/villain of this movie? Virtually every character in this is some kind of anti-hero, and that makes it hard to choose what side to be on. The investigator trying to uncover the smuggling ring is unlikable and the pirates/smugglers themselves aren't obviously the nicest people around. As a story, I was drawn into what was happening, but wasn't able to find myself emotionally engaged at all. The "horror" scenes are fun, but inconsequential. This is very much a Hammer production, and you can tell from the silly hair, awesome sets, and just the look and style of the way it was filmed. But sadly, as much as I love Hammer movies, this isn't one of the better ones. I enjoyed it enough, and I always love seeing Peter Cushing (and Oliver Reed), but as a whole I feel they could've done better with the characters.
Who would I recommend it to? People looking for some unconventional Hammer or pirate movies might enjoy this.