Modern Who's magnum opus. I don't think it ever got any better than this; a beautiful adaptation of the classic Dickens tale, but done in a way that feels fresh and fully involves the time travel aspect of the story much more than the original could.

The music is fantastic, the world building is amazing. Ember and Sardicktown are, perhaps, the greatest realised alien planet of all of Doctor Who; it feels so lived in, unique, fun to explore if you ever visit. Its aesthetic is unmatched, its people have a consistent feel that isn't generic or typical. Such brilliant set and costume design.

The story is emotional and involving, you just get sucked into this world for the hour and it never lets you go. It's one of Matt Smith's greatest performance, and it helps that the Doctor is so perfectly characterised within this episode; he's given so many great lines and is fully engaging throughout.

You can't ignore how well the guest stars are doing to back all this up; Michael Gambon, Katherine Jenkins, Laurence Belcher and Danny Horn all deserve praise here.

It really is just the perfect coda to what I believe is the greatest Doctor Who series of them all - Series 5.