For a show that can go anywhere in time and space, 21st Century Doctor Who is strangely parochial. Its concerns are those of a WEIRD culture - Western, Educated, Industrial, Rich and Democratic. Our own planet has far more ways of seeing the world that Doctor Who is showing us, let alone the rest of the Universe.
In The Star Beast Donna asks The Meep what its pronouns are. This assumes that The Meep's native language has the same type of sex-based gender system as English, and that The Meep has the same sort of hangups about that as Russel T Davies. But only about a third of human languages have sex-based gender systems, and over half have no gender system at all. In some languages, the correct pronoun is determined by things like age, social status and formality. Some languages hardly use pronouns at all - either because the information is marked on the verb, or because you omit anything that can be understood from context. Speakers of languages with sex-based gender systems often take the attitude that gender just part of the way the language works, no big deal. If you ask an alien what its pronouns are, a reasonable answer is "What the heck are you talking about?"
One 20th Century story that depicted a fictional society particularly well was The Robots of Death. The story is confined to a single location, the sandminer, but the costumes, the dialogue between the crew members, their job titles, and Uvanov's backstory paint a vivid picture of the wider society of Kaldor. Kaldor, we learn, is a society ruled (often corruptly) by the First Families, where elaborate headdresses and face-paint are used to show status and office. Someone from outside the First Families can rise to command on talent, but risks being made a scapegoat if the First Families want to cover something up. They are dependent on robots - robots might even be employed to bring up an orphaned child - but often uneasy about this and still value human insight. Its economy revolved around using mobile sandminer vehicles to harvest valuable minerals from desert sandstorms. Their unease about their dependence on robots sometimes develops into full-blown robophobia. The explanation given for this, "It's like being surrounded by walking, talking dead men," is psychologically plausible - it's what we call the Uncanny Valley Effect.
This brings me to one of my greatest disappointments with 21st Century Doctor Who. For a science fiction show, it doesn't actually seem to care about science. In Gridlock, the cars are all using each other's exhausts as fuel. That's a perpetual motion machine, and if you have any knowledge of physics at all, it breaks suspension of disbelief. OK, so things like the TARDIS are definitely Sufficiently Advanced Technology, but basing the technology seen in the show on sound scientific principles wherever possible could lead to stronger stories - the more you care, the better you write. When the show first began the "Educate" bit of "Inform, Educate and Entertain" was an important part of its brief, and to that end they had a scientific advisor to ensure that science depicted made sense. His name was Kit Pedlar, and he devised the Cybermen.
As RTD leaned more and more into outright fantasy, he wrote weaker and weaker stories as a result. An example of this is the Pantheon of Discord. In a Pantheon story, a godlike being turns up, along with a "harbringer" (who does nothing), giggles inanely, announces that he's the God of Something, causes havoc, and sets the Doctor an arbitrary puzzle that he has to solve to defeat him. I don't think any idea has ever been overused more quickly.
Another area that Doctor Who originally sought to educate people about was history. 21st Century stories with a historical setting are usually "The Doctor Meets Famous Person" stories. One problem with this is that the famous historical person has to be given a simplified, broad strokes treatment that ignores their real flaws and complexities, and the second is that it tends to implicitly support the Great Men view of history, which most historians consider old-fashioned at best. Seeing the lives of ordinary people in history has potential. The most successful historical character there's ever been was Jamie McCrimmon, an ordinary Scot who fought on the losing side of the Battle of Culloden, and went on to become the Second Doctor's companion.
Pure historical stories were abandoned by the BBC after the first few years of Doctor Who because audiences found them boring compared to science fiction stories. Aliens invading in the past can work better - The Visitation is a good example. However, getting the balance between the science fiction and history right can be tricky. Rosa and Demons of the Punjab both felt that they'd have worked better if you took all the science fiction elements out of them - incuding the Doctor.
Another setting we need to think about is contemporary Earth. I feel that this should be used sparingly (not more than one per season), and that when it is used, it should feel like the world we live in. Since Rose, RTD set stories in an alternative present, where alien invasions were increasingly common knowledge, ending up with UNIT having a huge skyscraper base with a helipad in the middle of London. Part of Steven Moffat's motivation for the Cracks in Time story arc was go get back to the feeling that Doctor Who could be set in our world. It's much more involving if you can make believe that one day you could meet the Doctor in the street, get mixed up in his latest adventure, and be invited for a ride in the TARDIS.
Character development is an important part of making a story feel real, and unfortunately, 21st Century Doctor Who has often skimped on this. According to The Writer's Tale, RTD likes to delineate a character in three words. As a result, his characters tend to be shallow and static. In his first term as showrunner, the only companion he gave significant development to was Donna, and he ended her story the first time round by undoing all her character development. At least he tried to right this in the 60th Anniversary specials. Steven Morrat's companion characters, Amy, Rory and Clara, were much better developed. We got to know them, we saw where they were coming from, and what their lives outside the TARDIS were like. We learnt how travelling with the Doctor changed them - sometimes for the better, sometimes for the worse. Clara's inherent compassion and her growing recklessness made her death in Face the Raven a shockingly logical end for her character.
Doctor Who has a long, complex and sometimes contradictory history, and has always worn its continuity lightly. However, it's important to retain some sense of coherence, and to this end writers should respect the work of their predecessors. You shouldn't contradict previous stories unless they're really terrible. Artibrarily retconning the Doctor's entire backstory, as Chris Chibnall did with the Timeless Child story arc, added nothing. An ordinary Time Lord who ran away and got involved in the wider universe is a better backstory than a mysterious immortal being who the Time Lords got their powers by experimenting on. And what did it give us? A mess of contradictions, a character who claims to be the Doctor but has none of the Doctor's values, and an episode that consists of one third the irrelevant life story of a boring Irish policeman, one third the Master giving a pointless infodump, and one third the worst Cybermen story ever made. The Timeless Child belongs in the same bin as "I'm half human on my mother's side."
It's a big, strange, scary, wonderful universe out there, and we've got a TARDIS. Let's go and explore it.
Good worldbuilding makes good stories.
