The good first: Karen Gillan is excellent. Amy already feels more three-dimensional than many of her predecessors. She has a disarming combination of confidence and uncertainty. I cheered when she picked the lock with the hairpin; I want to know more about the wedding, as does she. It's only two episodes in, but she is charming her way to the top of my favourite companions chart.
Moffatt does scary very well. The 'orrible tentacles, the sinister two-faced creatures, the hooded brethren, the repeated memory wipes, the terrified children, the queen with her untroubled glasses of water, all made a brilliant set of images. The fact that it all turns out to be something of a misunderstanding could have made the whole thing flop, but was handled poignantly (as in The Empty Child / The Doctor Dances.
Liked also: Sophie Okonedo, Terence Hardiman, the child actors.
A great lead-in to next week's episode as well, rather better than, say, the unseen time-space telegraph which summons the Fourth Doctor to a part of Sussex pretending to be Loch Ness.
The less good: Moffatt sometimes lays it on a bit thick. (Does anyone remember The Girl With Two Breasts?) The parallel between the fate of the Space Whale and the Doctor was a beautiful concept, but hammered home without subtlety.
There were also some significant plot holes, though perhaps I just wasn't paying attention. I did not catch how the Doctor and Amy managed to clean themselves (and their clothes) so rapidly after their Jonah experience. I was also left a bit confused as to who had set up the machinery of repression, and how. The whale itself, and its tentacular sensory extensions, seem to be completely separated from the Demon Headmaster and the brethren, who themselves of course are allowing the queen to go her own, potentially dangerous, way. It didn't quite hang together for me.
Also - and this is a peculiar point reinforced by having watched the episode in Belfast - the framing of the UK in the story is a bit problematic. The towers all seemed to bear the name of southern English counties - the remark about Scotland was ambiguous, no trace of Wales or Norn Iron. It will have played well enough in most of the mainland but jarred with me a bit (similarly the Ninth Doctor's display of British patriotism marrs The Empty Child / The Doctor Dances) and I wonder if it will really help in the export market.
Still, the good outweighed the bad, even if it wasn't quite up to the standard of The Eleventh Hour.