The Doctor's own role is not especially glorious in this story. Rather than concentrate on the dangers of the drilling project, he prefers to try and escape via TARDIS. When the Brigadier accuses him of having wasted time "gallivanting", the Doctor takes deep offence, but the Brigadier is absolutely right. Had the Doctor stuck around on our world instead, he could have simply badgered Stahlman to take his glove off, which would have resulted in his being instantly discredited. We the viewers know about the intimate connection between the drilling and the Primords; the penny never really drops for the characters.
It's a shame that they didn't give Liz Shaw a decent farewell scene. I suppose that is part of the problem of a season with only four stories and the last one seven parts. There was too much plot to fit in, perhaps. On the second DVD, Caroline John comes across in the interviews as a very pleasant and intelligent person, much more so than the last companion-playing actress who I saw interviewed, who came across as pretty brainless. But it's nice that the last shot of the series, and of the season, is of her laughing at the Doctor and Brigadier squabbling.
The story of John Woods/John Levene and his acting career is a rather nice one too, which I hadn't heard before.
More on alternate universes in another post. But in summary: a good set of DVDs.