In November 1963, the world got its first taste of Doctor Who. The first serial, often known by the name of its first episode “An Unearthly Child,” brought a pair of schoolteachers to a junkyard to investigate a strange student of theirs and wound up sending them careening through space and time. It set the formula for many stories to come, served as a key moment in the character arc of the mysterious Doctor, and is generally a must-watch for those who want to get a feel for the classic series.

What makes “An Unearthly Child” so great? Here’s my take on a few of the key elements.

Doctor Who just finished Season One…which is really Series 14 or Season 40, depending on how you count. The season offered many new features, from a new Doctor played by Ncuti Gatwa to more money behind the scenes courtesy of a deal with Disney. It also offered new (or at least underexplored) themes to the show, including a heavy lean toward the supernatural.

If there’s one thing that defines this most recent season of Doctor Who, it’s the theme of stories. The season is structured like a fairy tale, and the stories the characters experience–and one they invent–drives the narrative of the Doctor’s latest adventure.

To illustrate what I mean, let’s go episode by episode through the tale of Ruby Sunday.

Continued from last time, the Doctor ended his classic era as a fairly well-rounded individual…or as well-rounded as the Doctor ever gets, at least. Paul McGann’s Eighth Doctor was a culmination of the classic Doctors that had showcased the series from 1963 to 1989. He was brilliant, compassionate, quirky, and more open with his emotions than he had ever been before.

Then the Time War happened.

Between the 1996 TV movie and the 2005 series revival, the Time Lords of Gallifrey went to war with the Daleks of Skaro and nearly destroyed the universe in the process. Off-screen, the Doctor ultimately made the decision to destroy both sides, leaving him as the last of his people and carrying the weight of a double genocide on his conscience.

The revival era Doctor is basically a person going through the stages of grief. More dangerous and volatile than before, they were no longer a mere explorer but often verged on being a vengeful god–someone who wanted to save lives, but who could do terrible things when angered.

The Fifteenth Doctor has landed, and he seems to be the most emotionally healthy version of the character that we’ve seen in the show’s 60-year history. Still carrying his flaws and trauma, he has nonetheless shown openness about his past and a willingness to express his emotions rather than hide behind a stoic facade.

While the Doctor will undoubtedly have new traumas and occasional reversions in personality in the years to come, a relatively healthy Time Lord is a refreshing change for the character. It’s also a culmination of 15 different regenerations, each of which shaped him into the man he is today.

While the concept of regeneration is mostly a conceit to keep the show going even after the departure of a lead actor, the long-running nature of Doctor Who allows a bigger scope for character development than you typically find in serial fiction. Each of the Doctor’s previous incarnations made him the person he is today, and this is how.