It does seem to be strongly hinted that the "good man" that River kills is the Doctor. If that is the case though, why would she not remember that scene from her point of view? Well, maybe she does. And that still doesn't answer the question of why the Doctor felt he needed to die there, to be killed by an astronaut emerging out of Lake Powell. It's such a surreal moment; I really love it, but the questions are maddening. I really hope that the answers are worth waiting for.