I got all of it except the fact that he killed his wife and kid. I suppose it makes sense now, but I didn't piece that together. I'm still confused as to how all those photos got on the wall.

Simon's voice on the tape was clearly a man's, whereas the voices before were supposedly Mary's alternate personalities. The way Gordon kept being told to "wake up" made me wonder if any of it, except his murdering his family, had actually happened. I kind of wondered whether he was in one of those repressed memory sessions talked about, and the whole scenario with the hospital asbestos clearing was his mind's way to uncover the truth about murdering his family. Is that a crazy idea, or can anyone explain why Simon's voice was a real man's voice as opposed to a girl faking a male voice?

Simon is an evil entity that possesses people who are weak or some such, it's that last line in the film. Gordon became possessed when he first entered the hospital and you can hear Simon say 'Hello Gordon'

That's what the link said, and apparently that's what the director says on the dvd commentary. I just thought with the "wake up" "you're asleep" and "do it" that people kept telling Gordon, and the way Simon's voice was so masculine, that this was a horror film more like Identity than The Shining. I asked about this at IMDB too, and was told that I'm not the first person to think this, but it isn't what the director intended. Also, people say that one actress did Mary and all her alter ego's voices, including Simon's (which is amazing I think)