But this conception of the role is also a reversion, knowingly retro, a jumping backward in time over the heads of Smith and Tennant, to the spikier style of the greatest early Doctors, Patrick Troughton’s 2nd (1966–69) and Tom Baker’s 4th (1974–81).
The mode of what has now been officially designated "Classic Doctor Who" is firmly in the tradition of the troublesome British eccentric hero, which is bound to strike many in the show’s huge new audience as somewhat fussy and old fashioned. (Baker played Sherlock Holmes for the BBC, as well, and it’s surely no accident that “Deep Breath” is set in Victorian London.)
The story is also elegantly thematically consistent. If we wanted to get high-fallutin’ about it we could say that "Deep Breath" is about the masks people adopt and their relationship to their true identity. To put it another way, the central issue is: How much does the Doctor actually change when he regenerates? Is he an entirely different person or a variation on a theme?
Pains are taken early on to disabuse young Clara of the notion that the Doctor’s drastically altered appearance is a definitive indication that he’s no longer the goofy and engaging do-gooder she admired. That persona was merely a mask, she’s told, concealing his utterly alien true identity.
Of course the situation is tricky here because it’s a firmly established convention of the show that it isn’t just the Doctor’s face that changes with each Regeneration, but also his personality. In a powerful later scene, the Doctor himself confronts the issue, gazing into a mirror, shocked by the signs of aging on his new face, soliloquizing on its implications: "It’s covered with lines, but I didn’t do the frowning. Who frowned me this face?" And he wonders, "Why this one? Why did I chose this face? It’s like I’m trying to tell myself something. Like I’m trying to make a point. But what’s so important that I can’t just tell myself what I’m thinking?" (Masks are a motif throughout the episode, but we can’t run through any of the others without dropping major spoilers.)
Capaldi, I think, has the potential to become one the great Doctors, with a grave sense of wonder that could carry the show pretty deeply "into darkness," the destination announced in the trailer for his second episode. It’s an open whether the shinier, perkier current version of the show has room for that kind of greatness, any longer.