Tonight’s episode of Dr Who, the season finale, was a joyous confirmation of Russell T Davies’s status as the show’s reinventor. The key is in his regeneration of an old franchise that had gone to seed in the hands of people embarrassed to be charged with running a science fiction show for all the family, and the way it’s now positioned front and centre at the heart of BBC1’s role as a national and international broadcaster.

Make no mistake, in these days of shows tailored to demographics, and a BBC determined to establish a foothold in every conceivable social grouping, Dr Who is a hugely important series. While everyone else is talking narrowcasting, Russell has managed to reaffirm the importance of television as an experience shared across generations and subcultures.

Not only is Dr Who a show with a mission, it’s one with a message. It’s a series about the future of our species, and at a time when we’re bombarded with bulletins about global warming, economic downturn, intolerance and the rest, Dr Who is pointing to a multi-ethnic polysexual future in which difference is accepted and every individual can make a difference. A bit Pollyanna-ish perhaps, but I’d rather the next generation were growing up with that as a vision than whatever they’re gleaning from a diet of Resident Evil and Happy Meals.

OK, so every episode has not been one of unalloyed success, and some of Russell’s scripts have been among the clunkiest since the show has reappeared. But when he does well, he does better than well, and this evening’s barnstormer was an example of why Russell T Davies deserves whatever accolades can be sent his way.

In 65 fabulous minutes, the series finale managed to combine a thwarting of a(nother) Dalek plan to defeat the Doctor and destroy the universe with a whole bunch of subplots relating to the extended family of companions and chums that he has accumulated since coming back to our screens. Everyone got their moment, from swashbuckling bisexual Captain Jack to Bernard Cribbins, in his role as Donna Noble’s grandfather. And Donna got the biggest moment of all, which fully justified her surname: Everywoman became Wonder Woman, if only for a short while, before the cosmic clock was reset and all returned to normal. There’s nothing more noble than a sacrifice like that, and sacrifice is what Dr Who runs on.

Oh, and Rose came back, had to return to her parallel world, and did so in the company of the Doctor, or at least a half-human iteration of The Doctor, who’ll be able to settle down and live and love and die with her as a mortal. What more could you ask for? You can’t accuse Davies of skimping on emotional scenes, and he relished every opportunity to shoehorn them in: anyone who watched the show without a tear coming to their eyes at some point is a Cyberman, for sure.

Juggling those emotional pay-offs with the structural demands of the plot was a hell of a feat, and demonstrated Davies’s abundant skill as a writer at the same time as getting across his underlying belief that quality drama can be life-affirming…too many people mistake misery for seriousness, and if Davies demonstrates anything it’s the power of truly popular drama to touch the lives of its audience.