Saw it last night; really good movie. I was disappointed that the eyeball guy only had one scene and that it kinda drifted away from its fantasy plot for a while, but overall I was satisfied. Spoiler, highlight to read: I was really impressed that they had the guts to kill off the protagonist, and one who was a kid, no less. It sort of reminded me of Jacob's Ladder in how the death was more of a relief from what they were going through. I think I'll need to see it again to analyze the crap out of it.
I have no idea why people are complaining that it's inappropriate for kids, though. It has that R rating for a reason, y'know.