The "story" part - ie not the trial - of the Mysterious Planet is Doctor Who at its most average. There's chase scenes down corridors, big robots, and side characters in silly outfits. Whilst I wouldn't go as far as to say they've figure out how to write Peri, someone has realised that audiences prefer it when their two main characters seem to like each other, which is a very nice change from s22.

The trial section is more fun, with the Valeyard, Inquisitor, and Doctor all playing off each other. It's not, like, groundbreaking television, but it is such a welcome change to have a Sixth Doctor serial (or part of one) that could reasonably be called "enjoyable"