Well, that was rather obvious, wasn't it?
Not to say that I didn't like the episode, because I did. It certainly produced an emotional reaction (several, actually.) But there's something about Moffat's writing... it's like he has a giant checklist that he ticks off to ensure he creates the maximum effect. It's all very... contrived. With horror episodes like Blink, that's okay, because, well, horror works like that. But when it's supposed to have emotional resonance, I can't help but feel a little cheated. This all comes back down to me not being especially fond of deliberate, wanton manipulation in fiction. I like the idea of a little bit of chance, accidental truth; as opposed to prescribed deliberation on "what will make the audience 'oooooh' and 'ahhhhh'?"
And, of course, Moffat's a writer of several genres --- a very good writer of several genres, who knows narrative convention inside and out and understands exactly which buttons to press and levers to pull. Sometimes, this works remarkably to his advantage --- but sometimes, such as with Jekyll, or, uh, in my opinion, this episode, it weakens the stories he tells. Obviously not for everyone, but definitely for me.
I am aware I'm one of very few people who react like this. Most audience members actively like the manipulation. They expect it. They don't care if it's predictable --- in fact, the more predictable, the better, in some situations. Especially if it's done in such a way that they can say, "I predicted that!" But I --- I like to think that once in a while a writer says something profound without really meaning to. They didn't aim to make the audience shocked, or sad, or happy at that precise moment... but somehow they did. You get the feeling everything Moffat writes is for an express purpose, every tiny little detail --- and where's the fun in that? He leaves nothing to chance.
I've been a fan of his since I was a young kid, because he writes very accessible stories with great dialogue and usually solid, if not remarkable characterisation (he tends to rely upon archetypes a little too much), so maybe I'm still expecting the world from him. But I get more disappointed with that episode the more I think about it.