Scott Wise’s review published on Letterboxd :
Time travel is always a difficult subject to tackle. Not just for the mental leaps or paradoxes involved, but many obstacles to creating a compelling story around this concept simply get bogged down in the mechanics. Films with time travel at its core are rarely great or truly accessible because the tipping point between extremely-simple-but-logic-breaking (Back to the Future) and extremely-complex-but-brain-breaking (Primer) is as fine as a razor’s edge.
And that’s the startling thing about this Spanish sci-fi thriller: it walks that fine line so perfectly. It gives its audience just the bits and pieces it needs to understand the mechanics - the basics of the machinery, the general theory and flow of events - without letting any of them bog down the core narrative. The film's setting - a countryside home near an enigmatic research facility, each separated by a tangled woodland - is kept purposefully minimal, offering little conceptual clutter to distract from our understanding of the events.
Its cyclical story unfolds in multiple layers, each adding new information to the story. But here’s the thing: that doesn’t necessarily mean it gets more complex. It actually, at times, offers its own counterpoint as it simplifies one aspect while complicating another, building in an interesting give-and-take. And in the end, it’s all about as neat as it is messy.
Wonderfully scored with a classical approach to tension-building and beautifully shot, the film’s technical attributes belie its low budget. Its a testament to how much can be done with a fantastic script and a clear vision. It will be very interesting to see if the eventual Cronenberg-helmed English-Language remake will be able to walk the same fine line as the Spanish original, or if it will fall too far astray.