It's interesting but, despite all the evidence to the contrary (photographs, written interviews and so on - you know, actual hard evidence) I still wasn't entirely sure whether or not the Doctor was actually going to regenerate in the opening moments of Journey's End.
That said, I wasn't exactly surprised when David Tennant emerged from orange glow looking as healthy as ever. And i was somewhat releived when he did. I don't think I'm quite ready to see the Tenth Doctor leave just yet. Besides, this wasn't the right story for David Tennant's swansong.
Yes the story was big, yes it was epic and, normally that would be ideal for a Doctor's last story. But in this case it would be wrong because it wasn't the Doctor's story. It wasn't even Rose's despite all the build up to her return. It was Donna's.
It's quite something when, amidst all the Daleks, the multitude of returning characters, the equally-returning Davros and the multiple Doctors, Catherine Tate still manages to steal the show. Although she gives a great performance as TheDoctor/Donna (with a great impersonation of David Tennant) it's the final few scenes that really stand out for me.
It's easy to forget how far the character has come since she first arrived on board the TARDIS in her wedding dress. Here, we're given a reminder of the Donna of hold and it's genuinely to see her return to the person she was. As her grandfather says: "She was better!" Indeed she was and that really sums up the episode and the series in a nutshell. What the series has shown since the very beginning is that the Doctor changes people. He doesn't turn them into weapons, as Davros would have it. He changes their outlook on life and helps people to see the bigger picture. And in turn he learns from them and improves himself. As the First Doctor once put it: "As we learn about each other so we learn about ourselves."
So, in short, it was a great shame to see Donna leave in the way that she did. It will be interesting to see if her replacement can match up to her.