What's not to love about this episode? The baddies have a great creepy design - steampunk and the clockwork ticking. David Tennant and Sophia Myles obviously have chemistry to burn at this point in their relationship - and she's both quite a stunner AND quite imperial in her role as Chief Mistress. You buy that this is a person that the Doctor, one of the most extraordinary beings to ever live, would be fascinated by and who could captivate him in return.

The script is light and pacey, and self-contained, with a tragic romance.

The direction's quite good - several nice shots. The score is also lovely.

Also, this is one of the few episodes in this season that I think does justice to Rose Tyler, as it gives her Mickey to play off of - and Moffat writes her as quite spunky and capable of real generosity in this.