I really did not think it was that bad, the acting was not that bad for amateur actors, I felt they all really gave their best, and although not great, it was a good start for them. I think people just didnt like them using the similar monster from the abyss - But I dont see any issues with that.
I guess this is based on some old Spanish legend, and it was pretty weak but I have seen a lot worse many times. It did hold my interest through most of the movie, and there were times I rolled my eyes because there were some stupid moments, but nothing that i would condemn this film for. For a low budget film, it was actually pretty refreshing.
If you watch a lot of low budget films, this one might be worth the while. The actors were pretty good looking, the leading lady was pretty sexy too, which helped a bit too!