"The Happiness Patrol" comes from an unpopular and often-neglected era of Doctor Who -- the end of the original series, when ratings were poor and internal BBC support for the show was practically nonexistent. But in spite of all that, this is a pretty cool serial that deserves a charitable reassessment.
The basic premise is that the Doctor and his companion Ace arrive on a planet where sadness has been banned, and is punishable by death. The planet is ruled by the insane dictator Helen A, who is an obvious parody of Margaret Thatcher. (Amusingly, British journalists didn't notice the Thatcher parallel until 2010, when "The Happiness Patrol" was exhumed and re-examined by the media, and became briefly controversial.) Helen A's chief henchman is a robot, made of candy, who kills dissidents by drowning them in syrup.
Does all this sound a bit grotesque, perhaps even ridiculous? Well, it is ridiculous, of course. But for those who agree with the left-wing politics of this serial, and can enjoy its peculiar brand of dark humor, there is much to appreciate here. Indeed, I quite like the gutsy social commentary in the script, and I think it's still very relevant. Meanwhile, some of the serial's perceived weaknesses -- false-looking sets, over-the-top acting, and a general campy atmosphere -- become more acceptable, and perhaps even appropriate, when you view them through the lens of political satire.
As for the DVD itself, it's one of the best single-disc Doctor Who editions to come along in a while. It includes a making-of special that intelligently examines the serial's politics and production strengths/weaknesses, as well as an extensive collection of extended and deleted scenes (the highlight of which is a much better introduction scene for the character Susan Q). The DVD also includes a fairly long featurette on the politics of Doctor Who, which covers the show's entire decades-long history, touching upon all of the obviously political stories. This is a really interesting, substantive special feature of the sort that I particularly enjoy, since it goes beyond surface analysis of stuff like sets and special effects in order to unpack what Doctor Who is actually about. Good times.
So, in the end, I recommend both this serial and the DVD. This isn't exactly classic Doctor Who -- other serials have better writing and better production -- but still, this is an intelligent and underrated story, not a goofy camp-fest that deserves to be written off. The Kandyman alone makes this worth watching again; his costume is so demented that it must be seen to be disbelieved.