Roots: The plot is strongly reminiscent of both The Brain of Morbius and Time and The Rani. The Sisters are inspired by Puss in Boots and Survival. Chip is partly based on Gollum from The Lord of the Rings, as Rose comments. Zombie movies. MRSA. The larder scene is inspired by Tomb of the Cybermen. The Intensive Care area was reminiscent of The Matrix. There's a throwaway reference to Brain Stem Research, animal testing, and the ethics of cloning - all issues which shaped the plot. New New York could be a reference to Futurama, and probably plenty of other Science Fiction stories. The shops line is, of course, a reference to the fact that most real hospitals have shops, and the Doctor actually points to a real-world shop at the location when saying where he would put it. The line "New New Doctor" may be a reference to Tennant's stint as the second Doctor in the second incarnation of the series.
Goofs: When Rose steps into the lift at the start, she's in the right-hand one. When she steps out, she's in the left-hand one. [The lifts open on different sides on different levels.]
Why does Cassandra's skin just disappear when she takes over Rose?
The corpses are in remarkably good condition for patients who have been infected with every disease known to mankind. And they all seem to have identical symptoms, surely you wouldn't infect all of them with everything. And given that they were bred in isolation, how did they develop language and communication skills? [However, there is talk about them being linked through "the machine", so maybe this is responsible.]
If the lifts aren't working due to the quarantine, why are they still moving on the external shots?
Where does the sister on the ladder come from? She wasn't in the basement when the Doctor and Rose/Cassandra started climbing, and the patients are in very close pursuit.
Why doesn't the Doctor burn his trousers when sliding down the cable?
The cure is very suspect. Firstly, it's a mix of different drugs, and different drugs taken together frequently produce complications. Secondly, the drugs are intravenous drugs - even when mixed with other intravenous drugs and disinfectant, they shouldn't have any effect when passed on through touch. Plus, it's a bit of a lucky co-incidence that the small number of drugs in Ward 26 contained the cures to everything.
Why does Chip's voice change back to normal between Cassandra taking him over and the trip into Cassandra's past?
The Duke of Manhattan and the Face of Boe are actually in visibly different wards which have been edited into a single ward.
Technobabble: Cassandra takes over Rose by using a psychograft. A subframe can be unlocked with the installation protocol.
Double Entendres: Cassandra on the Doctor's body: "So many parts; hardly used."
Dialogue Disasters: "The flesh is free!"
Dialogue Triumphs: Cassandra: "What do you think I'm going to do? Flap you to death?"
Cassandra seeing herself in Rose's body: "Oh my God! I'm a Chav!"
The Duke's aide: "Any friendship expressed by the Duke of Manhattan does not constitute a legal contract."
Continuity: New Earth is in the galaxy M87. It has apple grass, which has a distinctive smell. One city is New New York, it is the 15th New York. technically New New New New New New New New New New New New New New New New York. The city has a population of ten million.
Members of the public are only allowed to gaze on the Duke of Manhattan with written permission from the Senate. Statements he makes may not be made public without official clearance.
Diseases of the future include petrifold regression - turning to stone, Marconi's disease (whose victims emit the morse code for SOS), and paladome pancrosis (which kills in ten minutes). The Tardisode trailer also mentions portray syndrome. The Tardisode also mentions Portray syndrome.
Cassandra survived The End of the World. She has a force-grown clone called Chip who is a "half-life".
The Face of Boe is dying of old age, but recovers thanks to the Doctor. The Doctor only met him the once. There are rumours that he is millions of years old, though that is considered impossible. Legend says that he has watched the universe grow old. One legend says that just before his death, he will impart his great secret to one like himself - to a wanderer, the man without a home, the lonely god. He is telepathic, and is the last of Boekind. He communicates by means of telepathy. He says that he and the Doctor will meet again for a third and last time. The Face's telepathic message appears on the Doctor's psychic paper before he arrives on New Earth.
A green moon is the universal symbol for hospitals. Psychografts are banned on every civilised planet.
The Hospital has gardens, where cuttings are not permitted. They have colour-coded identity cards for visitors. It is run by the sisterhood of plenitude, who are cat-people. The lifts contain an automatic disinfectant routine. When humans came to New Earth, the Sisterhood had promised to help. In their quest to cure diseases, they tried using clone-meat and biocattle, but progress towards cures for diseases was too slow, so they started their programme of growing the "patients" or "the flesh" to experiment on. These people have developed sentience and can pass their diseased state to others by touching them. The matron swears by the goddess Antorey.
The Doctor comments that they are going "further than we've ever been before" - suggesting that the Doctor has never taken Rose any further forward or backwards in time than this, or further away from Earth.
Links: Cassandra, her robot spider, and the Face of Boe all originally appeared in The End of the World - the events of which are referred to several times, with the Face of Boe also making a cameo in The Long Game. Petrifold regression is also mentioned in Stone Rose (though it's almost certainly Stone Rose referencing New Earth rather than the other way around). The Doctor and Rose appeared to stay on Earth for a while after The Christmas Invasion, although the TARDIS has moved to the playground with the Bad Wolf graffiti (The Parting of the Ways), so they may have had adventures in-between.
Extras: This story has an episode of Doctor Who Confidential. The BBC created a one-minute trailer called a "Tardisode" for each episode of series two, which were available to download on your mobile or watch at the BBC website. They also made a commentary track available online, although neither are still available.
Location: London, after The Christmas Invasion, New Earth in 5,000,000,023 AD, a party for the Duke of Thrace at some point in Cassandra's past.
Future History: When Earth burnt up, humanity got nostalgic, and founded New Earth on a planet with the same size and orbit. The cure for petrifold regression won't be known for about a thousand years after this.
Various other stories - particularly in non-TV media - establish that Time Lord knowledge is extremely limited beyond approximately 10,000,000 AD. However, the Doctor is clearly very familiar with the universe circa 5 Billion AD. [He's visited this era several times before.]
The Bottom Line: 'The sisters are hiding something.' A fairly weak plot connects a number of good scenes. Cassandra is a particular highlight, and David Tennant continues to make a good impression as the Doctor. However, the whole thing just fails to gel into something better than "average".