This is a big deal for the show as it brings about two dramatic changes; this is the first time since William Hartnell that "The Doctor" is noticeably older, and it's also the first time that the actor portraying the character has had an entire lifetime to watch and grow with the series.
In Series 7, Steven Moffat aimed to make the aesthetic of the show more cinematic, filled with a little more drama and an edgier filming style akin to theatrical cinematography and editing. In "Deep Breath," the Series 8 premiere, he finally accomplishes this goal. All those effects, combined with Capaldi's humorous and energetic performance and a fervor for dynamic and interesting story telling, the premiere challenges fifty years of the show and subjects it to a new era of change. Dare we say, drawing in a new breath?
The show's characteristic's have definitely changed with Capaldi now donning the role. Previously, Christopher Eccleston, David Tennant, and Matt Smith all had very strong similarities in their portrayals; a bit goofy, sometimes serious, often emotional, and in the end, they always seem to MacGyver their way out of any sticky situation with a bit of dumb luck, coincidence or cleverness. Instead of all that, Capaldi's Doctor seems to be on top of things. He's cold, calculating and intelligent. No flailing around making monologues about how great he is, or citing his past a reason to simply surrender to him. Instead, he actually impresses the audience by doing the unexpected and often doesn't explain how or why he chooses these actions, even when they present a moral dilemma.
To give you a good spoilerific example. The Doctor in "Deep Breath" seemingly abandons Clara in a room full of things that want to kill her, forcing her to hold her breath and attempt her own escape (unsuccessfully). Though he does return disguised, he leaves again to take the "head off the machine." Though for fifty years The Doctor's creed has been "no killing" in the unspoken promise he made to all his selves, at the end of "Deep Breath," we're left with a question that will ultimately shape the story arc over the next several months; did he push him, or did he fall? Is Capaldi's Doctor now capable of doing what's necessary, or is this a facade to entice excitement in the audience that will ultimately end up in a predictable after-school-special moment?
The question long on the minds of fans has been proposed by Capaldi which leads us to believe that the nature of the conflict will become much more complex than a simple yes or no answer could provide. "Clara, tell me, am I a good man?" Capaldi asks in the TV trailer. "I don't know." she answers. Chilling, and a bit terrifying to wonder where it will take us next. No more zany adventures, it seems, now the show is picking up speed for being comical, entertaining and as well, to some degree, serious.
Overall, Capaldi gave the performance of his lifetime into the premiere and has most definitely breathed new life into the series. Fans of another BBC series "Sherlock" will find it well, but it's unclear how the fan base who grew up with Tennant and Smith will react to this new Doctor. Only time will tell, but one thing is for certain, the life of The Doctor has changed, and so the series with it must as well.