Man; that ending was great, however crazy it maybe. Saying that, here is my equally crazy theory behind both the ending and the credits voice-over:
So, what if the whole of AC 2 takes place within another animus and its Desmond’s son currently in it.
It goes some way to explaining the two unidentified voices over the credits and their conversation. I mean what son wouldn’t have a heart attack when re-living the point where dad was forced to stab their (maybe) mother.
Maybe I’ve watched Inception to much... I’m not sure.