Oh dear! I've been dreading getting to this story. Underworld is the only story I've ever fallen asleep watching and my overriding memory of it is of lots of boring extras in boring grey/brown costumes running around in boring grey/brown tunnels. To be fair, the first episode isn't that bad, (although the spaceship set is a very drab and boring looking, and yes grey/brown), the special effects are pretty good and the story set up seems interesting. Tom, however, seems bored already and as the story progresses he seems to amble through the proceedings looking like he can't wait for the filming to finish so he can get to the pub! Witness the cliffhanger to part 2 where the Doctor is becoming engulfed in a deadly gas and he stands there twirling his scarf around, or the scene where he's decending into the Underworld and just looking boredly arond him without a care in the world. Apparently at this point in the series Tom was not getting on well with Louise and he barely looks at her once in this story.
From episode 2 onwards this story goes into a terminal decline once we get bogged down in the boring grey/brown tunnels (all done with CSO by the way as the budget to build some sets didn't exist) and the effects work is less than convincing with actors occasionally appearing to walk through solid stone and legs and arms bizarrley disappearing. The villain of the story, the Oracle, is very uninspiring, yet another "insane computer" an idea done much better in The Face of Evil, and the parralleling of the story with the greek myths of Jason and the Argonauts (P7E = Persephone, Jackson = Jason, the race banks = the golden fleece etc) is hammered home with no subtlety whatsoever. The acting is pretty poor as well, Alan Lake hamming up his role, and Jackson being terminally boring. Yes, "boring" is basically the word that sums up Underword for me. (Even the title is boring!)Tom's worst story by a country mile.