I had some problems with the story. For starters, there's the obvious way of saving those not infected - as long as everyone thinks you're dead, and you can't affect the timelines, what's the problem? Plus, this Doctor didn't try to communicate with the infection for too long before deciding to attack it - without a choice. Not the Doctor we've been seeing lately.
I also wasn't keen on the voice-over, after Adelaide solves things herself - it wasn't necessary. I don't see how Adelaide's solution would inspire anyone - just create questions ("How'd she get here?").
There were good bits, too: I liked the water effects (and a good, if failed, attempt by Rusty at doing a Moffat, and converting an everyday thing into an object of fear), and the quiet moments when the Doctor was talking about Adelaide.
katlinel described this as mostly being a setup for what's coming next month, and I think that's right.
I think Granny Weatherwax would describe the Doctor's behaviour as cackling.