Three out of five. (IM3 is my favourite of shell-head's solo movies and would get four at least.)
The rather narcissistic and possibly borderline sociopathic Angie didn't do my enjoyment of the episode too many favours, though that's a judgement of the character and not the actress. Props to the Doctor and Clara for the statutory kidnapping and nearly getting her killed. Better luck next time.
Didn't like the thing with the destroyed galaxy, as a supposedly science fictional show ought at least to demonstrate a rudimentary knowledge of science and recognise that if a galaxy is x hundred thousand light years away then you're seeing it as it was x hundred thousand years ago.
Anyway, kids and dodgy science aside it was an enjoyable enough romp, made better by the Doctor's chess game and Warwick Davis' very robust turn as Porridge. Not anywhere in the same league as The Doctor's Wife
and surprisingly pedestrian in tone and direction considering its authorship, but still a decent episode with some very nice visuals and a sense of fun.