As a relative latecomer to the Dr. Who franchise, most of what I know about its pre-2005 revival, on and off-screen, comes secondhand from what others have written about it.
Freelance historian Michael Herbert recently made a contribution to this body of work with Dr. Who and the Communist, in which he wrote about series' writer Malcolm Hulke, whose career as TV writer and novelist included a lengthy and prolific association with Dr. Who. Hulke scripted over fifty episodes of the series, and has credits on a good many more thanks to the revival's recent use of his creations, the Silurians. In discussing the show, io9 lists episodes from three of the serials on which he worked ("The War Games," "Doctor Who and the Silurians" and "Colony in Space") among the series' top twenty all-time best cliff-hangers, while also remarking Hulke's "penchant for three-dimensional villains who think they're doing the right thing," specifically noting that it "adds a lot of life to General Carrington, especially in the later episodes" of the James Bondian "Ambassadors of Death" arc.
Hulke also wrote seven of the tie-in novels, which have also been well-received. Indeed, io9's epic post "Every Single Doctor Who Story Ranked From Best to Worst," rates Hulke's novelization of "The Colony in Space" as "way, way better" than the episode "because it fleshes out these one-dimensional characters who keep getting locked up and escaping on television." (That particular book can be hard to track down, but thanks to a Kindle edition, those curious to check out Hulke's novel-writing can easily lay their hands on Doctor Who and the Cave-Monsters.)
You can read more about Hulke's career, and Herbert's writing about it, in Herbert's guest blog post over at Bernadette Hyland's Lipstick Socialist, the Dr. Who news, opinion, reviews and podcast site Kasterborous, and of course, over at the web site of the volume's publisher, Five Leaves.