These specials not only were there to give Tennant the send-off he so rightly deserved, but also to help the series runners manage the transition to a new head-writer, as well as casting a new Doctor.
On the one hand, Tennant’s Doctor is a pleasure to watch, and they give him plenty of space to run around and spread his particular brand of insanity.
But by the time of the seventh episode, "A Good Man Goes to War," the quality storytelling had won me over and I was totally hooked into Moffat’s vision. I saw how terrifying it is when the light-hearted man turns deadly serious.
That's a lot of extremely inventive television and I didn't even mention the episode written by Neil Gaiman, "The Doctor's Wife," which is one of the high points of the show's Forty-Nine year history.