This actually feels like a dream Obi-Wan would really have. I can see totally see him feeling guilty about having to keep Anakin's son a secret from him, (even though it is for the best of the galaxy) as well as for Anakin's fall to the Dark Side. The fact that we can see him crying at the end just makes it even worse. It's really sad seeing how this dream goes from being a pleasant conversation between two friends, to a scary confrontation between a Master and his fallen Apprentice. (Even though the feeling that something isn't right about the situation is present throughout their whole exchange.)
