I have a huge fondness for New Earth, it's the first full outing for Tennant and Piper, and it's a very good one.
The Doctor and Rose travel further then they've ever gone, The Doctor explains what happened to Earth after its destruction in Episode 'The End of the world,' hence 'New Earth,' and it's not long before we're met with a friend and a foe from that episode, The Lady Cassandra and the face of Boe are both patients at a hospital run by cats. They have the ability to cure impossible diseases, but how? Intensive care is a particularly unpalatable place, so the Doctor is dealing with two enemies, Cassandra and the Nurses.
The cast is outstanding, each of the cats, Dona Croll, Adjoa Andoh and Anna Hope are so good, those costumes must have been tough to wear. Billie Piper is excellent, Cassandra's transformation into Rose is hilariously done, from class to brass. Sean Gallagher is fun as Chip, but my favourite performance comes Cassandra's character through the different actors, her death scene is stunningly done, so moving.
It's not an epic story by any means, and the ending is a little light, but overall it's just real good fun and utterly original.