[My arms too long SPOILER] First of all, really creepy when it got going, though for a few minutes I wonder WTF was going on when I saw the Doctor and Donna having two separate conversations, assuming the show was jumping back and forth in time.
I realised that the Doctor had left Donna behind, and worried that he won't save her, wondering if this would continue into the next episode, so was glad when he went back and saved her.
A few other questions: * I wonder why they showed the Isaac Newton bit? Seemed like a throwaway comedy element, but I hope they are going to develop it into a bigger plot; a whole episode about Newton and his "mavity" would be great; * The ship's captain - will we find out more about who she was? It seems a waste to introduce a character who is already dead, so will we find out all about her back story? I hope so.
And it was great to have Wilf back, just getting the see the late Bernard Cribbins.