9. Space Babies
"Space Babies" was the first proper episode of Russell T. Davies's second term as showrunner, which meant it had a lot to live up to. Unfortunately, the episode felt like it should be a filler, rather than a season opener. When the Doctor and Ruby ended up on a spaceship full of intelligent babies, they found themselves facing off against the Bogeyman.
This story fits alongside some of Davies's more contentious episodes from previous seasons, which often have to do with children and ridiculous concepts. While some fans have enjoyed the more absurd episodes in the past, there's not much of a plot to speak of in "Space Babies," and the villain ends up becoming so clumsily entangled with the episode's themes that it is neither scary nor profound.
While there are wonderful moments in this episode, particularly when the Doctor reassures Poppy that "nobody grows up wrong," it doesn't contribute much as an individual episode or part of the season-long plot. Because of its placement in the season, "Space Babies" needed to be an unquestionable success, and it just wasn't.