Don't get me wrong – Jon Pertwee was great as the Doctor.
But episodes from the 70's have dated horribly. And this one is set in Wales. One of the most difficult things to overcome in an episode like this, or the one from the Colin Baker era “Mark of the Rani”, is the Welsh accent and dialect. For those of us not used to it, it can sometimes obscure the plotline. And, the villian in this one is laughable. I mean that in a bad way.
Jon Pertwee is truly the saving grace of this one – and I must say, the special features contains a section called “Global Conspiracy!”, which is brilliant to watch after the episode.
If you are a Doctor Who fan, it's tolerable, if not, you won't be buying it anyway.