It’s talked about a lot as a scary film, but honestly, it isn’t particularly frightening. It feels more like a real-life drama centered around an event that... possibly never actually occurred. I have my doubts about the veracity of the events depicted. The biggest issue is that it attempts to reveal too much on screen. The initial assault wasn't effective, and while the shaky camera work and quick cuts initially created a somewhat unsettling atmosphere, the subsequent efforts to incorporate special effects just made things look cheap. This would have been far more successful if it had kept its scares hidden in darkness. That said, it is quite good at creating tension and suspense. It leaves you feeling anxious and on edge while watching, which is precisely why I choose to watch movies like this—to elicit a strong emotional reaction. In this case, instead of fear, the film generates nervous paranoia... and that’s just as satisfying; it achieves its purpose. The cheesy effects are distracting. While one might argue that the technology simply wasn't advanced enough at the time to create convincing visuals, I don’t buy that explanation—even now, those kinds of effects fall flat. What works is suggestion, allowing viewers to use their own imaginations to generate real scares. Regardless, it still manages to build suspense and provoke a sense of unease in the viewer, which is why we watch these types of movies, and it does so better than many others.

Source on TMDB