Finally a new Doctor Who, we've had to wait long enough for it
The story started out bugging me quite a bit, it's perhaps symptomatic for the current Doctor Who as it all just seems the same thing done over and over again, they run, something happens, they start to run again, ...
The story was seemingly similar to a two-parter of the second season, the episodes where they are near a black hole and they seem to have released the Devil himself. It's similar as it's a group of people, on a hostile planet (ie: in a space station) and one of their members is taken over by a hostile entity. The rest of the episode is basically trying to figure out how to escape and just what happened.
But at least this time, they added a bit more to it. The dilemma the Doctor faced was interesting and as there was no companion to play his conscience, it's quite interesting how they finally sort of made him snap.
My biggest regret is ofcourse that they didn't make his "Time Lord Victorious" attitude last longer, perhaps make it the basis of his ultimate death, which is ofcourse just one episode away. I will miss Tenant as the Doctor, he's done it with flair! Can't wait for that episode though, the return of my favourite villain, again but who's counting?
All in all, a good episode, dark and interesting.