Yeah, that was definitely an interesting episode. I'm not sure what's going on with the Doctor's potential past "former self," but we've seen a "fake Doctor" before - the Tenth Doctor faced that guy with the hot air balloon who thought he was the Doctor after having been accidentally "contaminated" with the Doctor's memories - although this seems very different. And the chameleon arch is in play again, too - interesting. I guess we'll have to see how it all plays out. I do hope they're not planning on grafting in a whole lot of former incarnations of the Doctor that have faded into obscurity; while it played out well enough for the War Doctor, I'd rather they not continue to go the retroactive continuity route. But we'll see.
Johnathan