Better than 3 1/3 stars; Lovecraft fans should enjoy it
The production values on this movie are not the best but hardly poor. The main problem will be obtaining a clear copy of the film. I have the version that came with my "Sci-Fi Classics" 100 movie pack.
As noted by Sol, the cast is surprisingly strong. James Earl Jones is a joy to watch and basically carries the movie, while Kove provides manly support and Jose Ferrer lends additional credibility. The balance of the cast is made up of women who are either hot, competent actresses, or both. Also, many non-professional actors (ie, Greek locals) add depth to the story.
Fans of Lovecraft's stories or Lovecraftian movies like "Dagon" (which bears a striking resemblance to Blood Tide in many ways) should enjoy this one. The atmosphere is terrific, especially being shot in the Greek isles. The acting is strong and the story builds suspense. The effects are minimal, which allows the watcher to create frightening images in their own imagination. There are a few very brief creature effects that are mediocre.
Modern horror films depend on thin plots, CGI effects, and nonexistent performances. This film is a throwback to early horror, when performance and atmosphere came first. I'd rate it fairly high in comparison to stuff like "Saw" or "Cloverfield."