Great game, I love the use of the prisoner dilema. The enviroment is great, the prisoner is scary and the sound is really effective. The best detail is the camera movement, it is really smooth.
I think you should adjust a bit the numbers. At the moment, you only gain 3 points for betraying, so if you always trust, at the last round at 8-8 you don't have any incentive to betray. If you move it to 4, it would create a powerful dilema to betray your fellow friend at 6-6 to win instantly.
All in all, I enjoyed it a lot, and I would like to see the ending!