The first season of the new Doctor Who introduced the audience to a slightly unhinged Doctor who had to fight his own survivor’s guilt and the isolation that comes with being the last one of your kind. It also introduced Rose, who with her youthful enthusiasm and energy managed to ground the Doctor again, after he seemed to drift after the end of the Time Lord vs Dalek war.
The second season introduced a new version of the Doctor that was more stable (cocksure is another word that comes to mind), but also more openly aggressive than the last one. That said, in his darker moments the previous Doctor felt way more aggressive than David Tennant ever was. Both seasons so far had a climatic battle with the Daleks at the end: first with a new Dalek armada created by the surviving Dalek emperor and second by an ark full of Daleks that had survived outside of space and time. Also Rose Tylor was stranded in a parallel reality at the end of the second season.
Which brings us to the third season, which gave us a new companion and a new threat at the end, which was mentioned by the face of Boo in the third episode. But like the other two seasons, the overarching story was merely an assortment of whispers and clues that lead into the finale, while the rest of the season consisted of mostly stand-alone episodes that ranged from weak to great (thought more great than weak overall). Freema Agyeman as Martha Jones had the bad job of playing the lovesick companion who is constantly compared to Rose, which means that most people will remember her as a cheap Rose substitute, which isn’t fair and to me screams lost potential. Also the entire “The Doctor is the best thing since sliced bread” does become annoying and should have been dialed down (sadly it never is, as far as I can see from recent seasons).
On the other hand, I really loved the finale, with the crazy Master coming from the end of time to conquer humanity with its own ancestors to create a new Time Lord / human star empire that defies temporal consistency by using the Doctor’s time machine as a paradox machine. It’s comic book logic in all its childish but also imaginative splendor. It’s the best sort of wonderful nonsense that Doctor Who has repeatedly offered. It asks you to quell your critical mind, to take the most ridiculous schemes and character motivations at face value and in return provides you a few hours of wonder (sometimes mixed with horror).