Just finished this and I can't really do a full review of this, if only because I don't know how to do justice to this without giving too much away or ruining it. This is a horror film, but not a gory film. There is a little bit of blood, but you're not going to see any eyeballs gouged out or guts munched. This is more in the mode of The Shining, where careful cinematography, meticulate design, and natural performances build a slowly unsettling world.
If you need a plot description, Tom and Evelyn (Lewis Fiander and Pruella Ransome, a couple of English actors whose other screen credits are mostly BBC series appearances) are a happily married couple on vacation in Spain, enjoying a last vacation away from the kids before the heavily-pregnant Evelyn gives birth. They're not too happy with the crowded, noisy city of Benavis. I wouldn't blame them, because dead, mutilated bodies are washing up on the beach the day they arrive.
So they head over to Almanzora, where Tom spent some time twelve years ago. When they arrive, they find the town pretty much deserted except for some children. In fact, if it wasn't for the children, they might think that everyone had disappeared...
If this sounds a little cliche, don't worry. Serrador does an excellent job of building tension without resorting to those cheap "cat jumps out of a room" kind of tricks. Once again, like "The Shining", this is a film that plays with silence and a pared-down soundtrack, that carefully frames shots for subtle effect. Most important, this is a movie where every single death registers (and I do mean EVERY SINGLE DEATH), saddens and horrifies. This has to be one of the few horror movies I know that starts with a news montage about (at the time) contemporary political atrocities without seeming pretentious or cheap.
Fiander and Ransome also deserve from credit. They play a married couple that argues and has problems without making them bickering or forgetting their love for each other. And when they make poor or selfish choices in the film, it's not because of stupidity or script contrivance, but because of everyday human emotion.
In fact, the only problem I had with the film is that the last forty minutes lack the sense of originality the first seventy had. There are still some great scenes (the first time the titular question is answered, for instance) and every moment is competently done and believable, but it moves into territory both Romero and Hitchcock have already explored. And the very last few minutes are guilty of dialogue that is a little too on-the-nose...
But please, please, please add this to your Netflix queue. The only place I've ever seen this reviewed was on Fangoria, and it does not deserve that level of obscurity. It's not even gory! Just terrifying on a moral and spiritual level.