This one has a few problems.
The Daleks’ behavior is highly implausible. I appreciate the attempt to explain it with their love of hatred, and their fear, but those are also implausible. Daleks do not preserve damaged individuals, and they do not ask for help.
On the other hand, a roomful of Daleks chanting ‘save us’ is pretty darn creepy.
A completely automated asylum planet with a defense system that can only be operated from within is implausible. Why would that feature exist on a world with no supervisory personnel? Why would it be made available only to the inmates? The conversion of humans to Daleks is strange. What use would Daleks have for a human form? They have no need for stealth or subterfuge. It adds to the creep factor but detracts from the story.
The dissolution of Amy and Rory’s marriage is not implausible in itself, but the explanation given is. I know that Amy has always been self-centered, but the idea that 2000 years is nothing compared to her mood swings is a bit much even for her. Kicking him out and pretending it’s for him is a bit much even for her. I can buy, and might even be interested in, a troubled marriage, but this one is too out there. Yes, I’ve heard the ‘infertility is complicated’ bit. Make it complicated, then. Don’t turn their problems on and off like a light switch. It’s insulting to the characters and anyone who’s been in their shoes.
Oswin is the gem of this episode. She is bright, funny, interesting, and tragic. Clara retained some of her traits in other incarnations, but I wish she’d held on to more. Junior Entertainment Manager for the Starship Alaska, shipwrecked on her first time out, is a much more compelling character than modern Clara ever got to be.
The Doctor too is fun here. It’s a delight to watch him figure things out. Matt Smith’s face is magic. And the reveals are gold. I remember watching the first time, how hard the truth about Oswin hit. It’s beautifully done; even expected, it still hurts.
Overall, the episode is standard Moffat fare. Ideas are poorly fleshed out; plausibility is stretched for story opportunities, with limited success. Too much idea is crammed into too little space, with not enough structure to hold it up.
However, it’s all worth it for Oswin Oswald.