It looked nice at the start. It was an interesting idea. But then they didn't actually tell much of a story with that idea? The kids were annoying. Weren't they too young for alegebra (although it's been a long time since I was in school and maybe I just don't remember ever being that young or something.) Why was a maths teacher having a sleepover in a museum anyway?
Danny looked bored for most of the episode, still has no chemistry with Clara, and defeated a tiger (which had no reason to be in the episode other than to put a tiger in the trailer) with a torch. It beat that time he did a flip over a robot anyway.
I guess it's lucky the tiger didn't go on to maul anyone else! But there seemed to be no one else in London other than the kids and the terrible mother actress on a bike. Don't millions of people live in London? Wouldn't they be out investigating?
Nelson's Column came down, animals escaped from the zoo...millions of people died in car crashes worldwide I guess? Did the trees going away at the end undo all this destruction?
I'd rather they hadn't had Missy in at all as the pointless cameos just make her less mysterious. She's gone from a guardian of the afterlife to a woman watching Doctor Who on her iPad.
Capaldi had some funny lines, but nothing would have been changed if the Doctor hadn't been in the episode. Okay he got the kids to make phone calls to tell the world not to burn down the trees...the trees that the episode had already established couldn't be burned down. Oops.