I felt that, for a lot of the time, Ben's contributions were somewhat sycophantic, with the occasional interesting question, and cheering post for a very under-the-gun Davies - so the ending was even more of a surprise.
There's (IIRC) the entire scripts of The Voyage of the Damned, Partners in Crime and Stolen Earth/Journey's End, in various states of revision, which is a thoroughly marvellous thing to see. You keep reading the final revision, seeing how it's improved, but thinking, "hmm, wasn't quite what I thought it was." And then finding yet another edit just slipped in at the last moment.
But you know what's most surprising?
RTD is really good at cartooning. His Tennant is brilliant.