Review of all 4 episodes:
The first episode is, in my opinion, a lot better than this story's reputation would lead you to expect. It comes across as an intelligently scripted, interesting political allegory. The story features the humanoid Gonds being exploited by a strange alien race known as the Krotons. This is the first script from future Doctor Who writing legend Robert Holmes and his talent is already starting to show in episode 1. However his talent is less visible in episodes 2-4. Another great talent and Doctor Who legend involved is Philip Madoc as Eelek. His great acting skills are not fully utilised but, of course, he portrays his part perfectly.
After the very solid start the following three episodes turn into just a slightly bland, not massively interesting 'filler' between more meaty stories in the season. It also suffers from technical limitations of the age and budget. The Krotons themselves look and sound very unimpressive.
The final verdict has to be this is decently scripted and acted but unremarkable. It is a disappointment, taken as a whole, after a promising 1st part.
My Ratings: Episode 1 - 8/10, Episode 2 to 4 - 6/10
Overall: 6.5/10