The first reaction I had to this film was - "an overkill". So much gore and blood in a small love triangle story, seemed excessive. But my very next thought was, I must be missing something. And as I went over the perfectly designed gory details of the movie one more time in my mind I realized I was watching a surreal fable on the fate of Spain from the Spanish civil war onward. The only proof of that claim I can give here without adding a spoiler is the fact that the opening scene of the film takes place in 1937 while most of the story happens on 1973, but there's no logical base for such a big time gap, the only reason these two dates were chosen is because the second is the mirror image of the first, and they both fit into the historic background necessary for the story.
As a fable, we have all the right ingredients of a fable in, the characters may be slightly flat, since their symbolic value is more important than their personality but the actors make it work anyhow.
So if your stomach can take gore and blood in quantities that would suit a horror movie, and you're interested in an original point of view on the destiny of Spain in the 20th century - it's definitely worth seeing