Throughout Tennant's tenure there was a real sense of consistency. Individual series felt distinct thanks to the rotating roster of companions, but that was a different ingredient rather than a rejig of the whole recipe. When Matt Smith took over the five-year old Tardis console room was redesigned to signal a new start for the series. That now feels a bit trivial because a reboot of the show seems to happen every year or so. Following the 'death' of Amy and Rory the Tardis got another redesign to something more old-school sci-fi, then, only ten episodes later, the Capaldi era kicked off with another design; we've had three new interiors in the time one existed uninterrupted. It may seem a rather trivial, but it just serves to make the box (and by extension those it contains) increasingly less familiar. We all remember the Ninth and Tenth's Tardis, with its almost bone-like pillars, and the first redesign for the Eleventh felt like a more extreme version of that. But after that it's all vague; the post-Amy redesign was notable for being silver, while Capaldi's look so similar had Clara not pointed it out we doubt we'd have even noticed. Along with the ever-changing opening sequence (what is up with the current one's clock faces), quite why the show keeps doing it is unclear. It may be an effort to boost ratings ("youhave to see this episode, there's a new Tardis"), although it could be a much more cynical merchandising decision.
