"The Sontaran Experiment", by Bob Baker and Dave Martin, achieves exactly what it sets out to achieve: to provide a diverting two-part filler story to plug the gap between "The Ark in Space" and "Genesis of the Daleks".
Fifty minutes really isn't a lot of time for the classic series to work with, and as such the plot (and resolution) is fairly straightforward. Of much more interest is the fact that "The Sontaran Experiment" was shot entirely on location, in cold weather on the windswept expanses of Dartmoor. There are, therefore, no corridors for once, and good use is made of the natural environment, with its dramatic vistas and all its concomitant hazards.
In his first performance as the Doctor under new producer Philip Hinchcliffe ("The Sontaran Experiment" was made before "The Ark in Space"), Tom Baker nails the part right away, delivering just the right mixture of madness and intensity. Companions Sarah Jane Smith and Harry Sullivan are their usual likeable (if hopeless) selves and there's nothing really to object to, except perhaps for the rather cheesy robot. The Sontaran makes a good, if one-dimensionasl villain, and his eventual demise is fairly gratifying.
The DVD presentation in this likeable slice of filler is the first of the BBC's cut-price "vanilla plus" presentations of classic series stories. The DVD therefore features a commentary (with actress Elisabeth Sladen, producer Philip Hinchcliffe and writer Bob Baker) and a decent documentary on the role of the Sontarans in Doctor Who, but not all that much else. A decent purchase for Who fans none the less.