Cold War, is in my opinion, an underrated episode: it kicks off with action right from the start and never lets go, and the Ice Warrior is brilliant. The menace that it brings actually feels like a real threat, as it picks off crew members in a way very reminiscent of Alien. Both Professor Grisenko and Captain Zhukov are enjoyable as well, and the scene between Clara and Grisenko as he asks about Ultravox a nice change of pace from the frantic nature of the episode. It sets out to do what Dalek did in 2005, and although it's not as good as Dalek it does do it well. The setting is gorgeous too, the sinking submarine providing a claustrophobic atmosphere in which this tank of a martian is running riot. The decision to show what the Ice Warriors truly look like was a big risk and it mostly payed off, even if the CGI looking a little bit dodgy. On a side note, if you own the Series 7 DVD or Blu Ray the commentary to this episode is brilliant.