If you're going to do a set of character pieces on Doctor Who villains, Davros is an obvious choice. A man willing to destroy his own race is an obvious candidate for a story that dives into his psyche. And Lance does a phenomenal job here.

A theme across this trilogy is that each story is telling two stories: one in the present, with the Doctor thwarting the latest evil scheme, and one in the past, describing the villain's origin. This is partially guesswork on my part, but I assume Master follows the same formula. And, if the trend holds true, then the present section of each story also prominently features the villain going through some sort of mental break which ends with them reaffirming who they know themselves to be.
Unlike the other entries in this trilogy, Davros also has an extra job to do, as there are stories with him set after this (again, assuming Master doesn't try to set up the TV movie), so a good chunk of the story is also devoted to laying tracks to set up Revelation of the Daleks, which I now have to rewatch.
Everything in this story comes together. The ties between capitalism and fascism, the hero worship in modern societies toward monsters of the past, the use of propaganda... just an incredible story which gets to the heart of everything.