Underworld was an ok serial. The cave interiors were pretty lame, they seemed to be early green/blue screen or something similar. It just looked pretty bad, and it didn't help the average story to have unimpressive locations. The story kind of felt like a bit of a retread of The Face of Evil, and it was a bit bland compared to that story. The gold headed minions were kind of interesting looking, but that was the only thing interesting about the villains. I liked the idea of a culture that the Timelords accidentally screwed up, but it wasn't a big factor in the story unfortunately. Overall it wasn't a bad story, but it wasn't very memorable. Next up will be the serial I accidentally skipped over, The Sun Makers.