Doctor Who special The Waters of Mars was, as promised, a darker episode than usual, with very little humour apart from Tennant's occasional clowning. There have been some great episodes that really play on claustrophobia effectively and this is one of them. The dark tone also applies to the fates of many of the characters - and the Doctor, who as usual is forced to make difficult moral choices, responds in a way we haven't seen before. Set on a human colony on Mars, Bowie Base One, the story featured zombie-like monsters - colonists' bodies taken over by an entity in the water. The set up reminded me of an old PC game, Martian Gothic - Reunification which is also about zombies on Mars.
If you also just watched the episode, you will know that the BBC played a trick on everyone in one of the trailers. Nice one! If not, and you're reading this within a week of the transmission date then The Waters of Mars should be available on iPlayer here. I am going to miss David Tennant.