David Tennant
There are just those people that can not get over the fact that David Tennant is longer the Doctor. Those people seriously need to get over it. If you were only watching the show for David Tennant, then you may not be a fan of and you do not get what Doctor Who is all about.
Doctor who is all about renewal, nothing is forever in on Doctor Who and even the Doctor gets a new face every so often. Part of the whole appeal of the show is who is the new Doctor going to be and how long will they be around for and who will replace them.
Besides there were three outcomes for David's time as the Doctor. The first one being what did happen, David decided that he wanted to leave on top when the show was still fun and he still loved it, the job and the Doctor. He did not want to stick around till it became a JOB!!! The second and third outcomes both involve David staying much longer then he wanted too, the fans wanted him too and the BBC wanted him too. If David had remained on the show for a few more years there is the possibility he becomes to comfortable or just too jaded, and that starts to effect his performance. Which he either becomes feed up with the show and everyone involved in the production that he leaves the show and has nothing positive say about the situation; or his performance starts to slip and fans soon start turning the channel which will cause the numbers to dip leading to the BBC removing him from the role.
So instead of bitching that David is no longer around, be happy for him. He got to live out his dream of playing the most coveted role in all of British television. If on the other hand you can not get over it and you just can't come around to support the wonderful young actor that is Matt Smith, then you may not be a Doctor Who fan and need to find something else to due on Saturdays. Matt has showed that he is worthy of walking in the shoes of the actors that came before that had the honor of playing the Doctor, from William Hartnell all the way to David Tennant.