I finally got round to watching it. There were bits that were great and then bits which were just beyond awful.
I liked the Sontaran - genuinely funny comic relief. I liked the cloud and I liked the evil looking snowmen. The Sherlock Holmes bit was funny and I liked the doctor's initial apathy.
I would have liked the villain to be more fleshed out. Some hint of redemption, some hint of doubt, some hint of his motivation. I think it would have been better if he had come to secretly hate the snow as he had gotten older, and if he had contributed to a resolution.
The end was beyond a deus ex machina. The only thing that could drown out the existing emotion in the snow is, of course, an entire family crying on Christmas Eve. I've gotten slightly tired of Moffat writing himself into a corner. It can be excused across an arc but not within an episode. Would have been far better if the villain had pulled the plug somehow.
The worst scene was the 'one word' scene. So ridiculous and pointless. If it wasn't bad enough to have the stupid 'answer with only one word' with no explanation of the point of it, Clara then somehow knows that 'pond' will get through to the Doctor. I'd bet that the entire subplot with the frozen pond came about because Moffat wanted a reason to put the word 'pond' in like that.
Overall, I think there were too many characters. The lizard woman and her wife were not needed, for example, and that time could have been spent making more of the villain.
I do like the Oswin riddle but have little faith it will be resolved adequately, as none of Moffat's other puzzles have been really.
Not sure how I feel about the Oswin character though. I liked Amy but I don't feel like we need an Amy clone - the only difference is that Oswin is also Sherlock Holmes. This might sound weird, but I think it's time for someone who is not so bipolar. Someone who doesn't lurch from prozac happy to crying all the time. Someone a bit calmer. It's weird as Donna is my favourite companion and is definitely not calm, but I want a change. (side note: out of all the episodes of companions embarking on their journey with the doctor, Donna's is my favourite).