Doctor Who is a series that always needs to try and appeal to all age groups, and it often works best when it gets a successful balance of between its scares and its more lighthearted adventure nature.
That's something it does well here, thanks to Moffat's script and some particularly excellent direction from Lawrence Gough. The relatively unknown director, whose previous credits include Misfits and Atlantis, has clearly done his horror homework, utilising his water creature to make for a creepy atmosphere and some effective jump scares.
That being said, this episode is not an outright scary one, but instead mixes that with a real sense of adventure, a fair bit of heart, and a lot of humour. We go to the end of the galaxy and back again, and along the way we get a number of genuinely laugh-out-loud moments and brilliant lines of dialogue, usually courtesy of one particular individual.