The plot itself isn't gonna make any top 10 lists but it's a great introduction to the UNIT era that immediately got me excited for what was to come. Liz is cool, the Autons have some pretty creepy moments, and this is probably one of the funniest Third Doctor stories I've seen what with the Doctor's regeneration sickness. Oh, and while it wasn't really on their minds at the time, the fact this was shot entirely on film leads to one of the best-looking stories in all of Classic Who.