There was a time, back when Doctor Who was on almost all year round, that all its principle cast members, including the eponymous time wizard, would go on vacation for a few episodes. Stories would be awkwardly restructured and characters temporarily written out to accommodate holiday plans. And invariably, the quality of the show suffered.

Nowadays, however, it feels like the reverse has become the truth. For it has been through absence rather than presence that David Tennant has made most of an impact in this year’s series. Simply, the best episodes have been those where the Doctor wasn’t there – or rather, not appearing as “the Doctor” as we have come to know him: be it reduced to a boz-eyed Gollum (“The Last Of The Time Lords”), gone undercover as Peter Bowles (“Human Nature/The Family of Blood”), or just simply not turning up at all (“Blink”).

This diminution has turned out to be the show’s salvation, by virtue of reminding the viewer that there is more in Tennant’s armoury of voices than just a loudmouth Cockney wideboy, and hence rendering his forays into Carry On TARDIS palare that little bit more bearable.

Upon the conclusion of 2007′s series, rarely has a primetime family drama flourished so much in spite of rather than because of the characterisation of its chief protagonist. John Simm, playing the Master, soared effortlessly above the narrative carnage of both this and the penultimate episode, single-handedly sustaining your interest and that of everyone else on screen, distracting everyone from the cavernous plot holes and meaningless technobabble, and reassuring all and sundry that Doctor Who could still be a home for heroes.

Conversely those scenes where Tennant was actually himself and not a walking cadaver or a parrot with giganticism revealed him strangely disinterested and almost bored. His great confrontations with the Master were neither great nor particularly confrontational, the first taking place on two ends of a mobile phone, the second on the strangely bleached South Downs.

Admittedly Simm had the better part to play and the best lines, but the name of the programme is Doctor Who, and Tennant’s emotional vacancy made his contributions perilously dispensable. Going off the evidence outlined above, maybe it would have been better entertainment-wise if he had stayed in absentia for even longer.

Although this was rarely the case in the old days, the new model Doctor Who has made it its business to deliver blockbuster finales. This year’s offering, then, was unsettling in its perversity: a dénouement aboard the Master’s floating battleship (what was this, Bedknobs and Broomsticks?) that compounded Tennant’s already leavened performance by swapping gritty science for gaudy spiritualism.

Somewhat incredulously, the Doctor – having spent the previous 12 episodes being variously Sid James, Bugsy Malone, Danny Dyer, Indiana Jones and Simon Bates during his tenure as the face of home video classification – finally turned into Jesus: resurrected from the dead via the power of prayer, growing invisible angel wings, then blessing his nemesis with teary forgiveness and a bear-hug. What happened to the bloke who believed in “no second chances” and cheerily kicked an alien of far less substance off the wing of a spaceship?

Perhaps that was the point – that meeting up with his “greatest foe” had tamed his hitherto brutal streaks. Or perhaps the point was that being turned into a spiky pensioner had taught the Doctor the value of reticence. Or perhaps the point was that love can save the world, with a bit of help from a Paradox Machine. Or perhaps the point was that there was no point and it was just done for effect. Send ‘em packing with a tear in their eye and a song in their heart!

Trouble was, having invested so much in the show, not just this year but each year since its stunning revival, you kind of hoped there would be one salient, consistent point to it all. Because to do otherwise would be almost, well, cheating.

Instead there was a bran-tub of outcomes and mixed messages (not to say numerous flashbacks – always a sign of an over-complicated, under-developed plot) to rummage through. And then, after that, came the teaser for the next episode, which almost immediately upstaged everything that had gone before. It wasn’t the first time during this series that what was still to come looked and felt a whole lot more exciting that what had just been and gone.

Supporting parts were always likely to be overshadowed with the Master in the script, but it was nonetheless disappointing to find Captain Jack – who used to be the motor of the Doctor’s adventures, here little more than a spare part – while Martha, having started the series promisingly as a companion with useful intelligence, only to become a sort of Jo Grant “what’s this for/what do I do now?” second banana, suddenly became a freedom fighter engaged in a massive worldwide act of double-bluff. And then, having saved the world, she decided to pack it all in, only not really, because she gave the Doctor her mobile. At least her family were kept as effective one-dimensional story devices rather than Jackie Tyler-esque pantomime dames.

Ah well. Maybe there’s a parallel here with The Simpsons, in that once a series has gone so far in one extreme direction, it’s impossible to retreat to where things started because to do so would be a sign of weakness. In this sense there’s no chance of, nor logic behind, a return to the low-key, primitively emotional tales of Christopher Eccleston. The days of making an entire cliffhanger out of the Doctor simply going, “Rose, I’m coming to get you” feel decades ago, not a couple of years.

Even so a situation where, whenever the Doctor isn’t the Doctor, you get the most entertaining and memorable episodes in the series, is not really a sound or comforting basis for the future. More time off all round? In certain people’s cases, permanently.