I thought it was okay. The plot was pretty thin, to be sure, the Doctor's pseudo-stalking of Clara and her parents through their lives was getting creepy, 'Grandfather', as one reviewer puts it, looks like a mummified version of Mr Hanky, and why did Merry psychically pin Clara to that cabinet like a little brat? But it was still an enjoyable story, with wonderful themes, an intriguing, if underdeveloped, monster, and pretty damn good effects.
However, I'm looking forward to the next episode, Cold War.
Have you seen the size of human brains? They're hilarious!
-The Twelfth Doctor