I love this movie.
I love the ideas it plays with, and I love how it's executed. Even though it's kinda low budget, it manages to bring across an air of mystery that is infectious.
I guess I've just always enjoyed stories that involve hidden worlds; things unseen by ordinary people. This film does multiple dimensions in style.
I think the moment I fell in love with it (as opposed to just enjoying it) was the scene where the protagonist goes to visit a member of the underground. It's at a point in the film where he's finally worked out that this is all very real and that he can't just walk up to the front door and expect to enter Rutger Hauer's secret hiding place. No. To get there, you have to take a left through the garden and walk between two innocuous trees. THEN open the front door, and you're there. Failure to follow this exact path means you open the door into some fat guy's apartment instead of the underground lair. Classic.
Ultimately, this movie is let down by the fact that in the final climax, good triumphs over evil by being just a bit more violent. But by the time you reach that point, you don't really mind. I reccommend it highly.