1. One of the best games i've played all gen. The art direction is superb, the action is intense and the methods used to tell the story (tape recorders, speakers, etc.) are excellent.
2. Somewhere in the range of 15 hours. Maybe a bit longer. It can be done under 10 if you don't try to explore the different rooms.
3. I haven't played through it twice, but I have been meaning to.
4. 9/10
5. I never tried the demo.