"Cube" or "Hypercube" was mentioned. I saw it recently and it did infact put a different spin on what we perceive as reality and time-space relations. My favourite horror movie of all time has got to be The Exorcist. I also like Event Horizon.
Currently, my university class in Cinema and Modernity is studying the horror genre. The reasons that people watch horror movies is what interests me. We have discussed in class how the "monsters" in horror movies are physical manifestations of fears or insecurities that we are otherwise unable to address. By displacing this fear onto a "monster", it therefore becomes defeatable. However, since the nature of our fears that we internalize never really cease to exist, the "monsters" continually pop up or rise again to haunt us. The analysis becomes much more detailed, but this is the basic idea.