Well, I shouldn't say "least essential". The "Doctor Who" DVD production team made a herculean effort trying to salvage this rather awkward little story. There's not much you can do to give the hard sell to a 45-minute episode from 1975 when releasing it on a standalone DVD. However, the folks at "2 Entertain" gave it their all. The story has been visually restored so that it looks as if it had been videotaped yesterday, and the few special features are meticulous.
Unfortunately, the episode being supported is not deserving of such kind consideration. "The Sontaran Experiment" was the first production from the Phillip Hinchcliffe/Robert Holmes producer/script editor team, which gave us a dozen of "Doctor Who"'s finest hours in the mid 1970s. As an opening act, this is not one of those hours. Featuring the return of the Sontarans, created by then-writer Holmes one season previously, "Experiment" features a villain not nearly as resourceful, clever or memorable as "The Time Warrior". The actor is the same but the writer is not, and that's most of the difference.
Since Sontaran actor Kevin Lindsey was in the final stages of heart failure, his character only appears in the final episode and doesn't get much to do. The rest of the story features the small cast running around a pile of rocks on Dartmoor. The rocks are very pretty. Indeed, the digitially remastered outdoor-broadcast video from 1975 looks fabulous -- this story could have been produced yesterday. Compare that with the feeble non-remastered look of the 1977 baseball World Series, recently released to DVD in the U.S., and you appreciate that this is a terrific restoration job.
The text commentary, as usual, is a lively affair written by Martin Wiggins, sharing with us some gruesome on-location anecdotes (mostly about Tom Baker's broken collarbone) and interesting discarded ideas from the story's first drafts (the mating habits of the Sontarans, and the British relics the authors intended should protrude from the Earth's surface thousands of years into the future where the story's set). The three-man audio commentary team -- Hinchcliffe, writer Bob Baker, and actress Lis Sladen -- share their crystal-clear memories from 30+ years ago. Compared to the commentary track from the sister DVD release (1969's classic "The Invasion") one begins to appreciate an inverse ratio between the quality of the story and the quality of the commentary.
The lone featurette produced for the disc is a comprehensive 39-minute history of the Sontarans. Called "Built For War", the documentary covers all of the Sontarans' "Doctor Who" appearances between 1974 and 1985, and thus features interviews with many people who had nothing to do with "Experiment" at all. Script editor Terrance Dicks (who did not script-edit this episode) reminisces about his relationship with writer Bob Holmes (who did not write it). Future Doctor Colin Baker (who did not appear in this episode) and future script editor Eric Saward (who did not script-edit it) take turns harshing on the 1985 Sontaran entry "The Two Doctors". The two men also take turns seeing who can reach 400 pounds first. Colin wins, although Saward grows an impressive mop of hair to finish in second place by a single ounce. Good heavens, Colin! The normally zaftig Dicks looks like Nicole Richie next to those two.