Captain Scarlet and the Mysterons (1967)

There are some obvious similarities between this show and later Gerry Anderson offering UFO, as both feature multinational organisations (called SHADO in UFO, Spectrum here) attempting to thwart a technologically superior alien menace.

There are differences, of course, the most obvious of which is that the later show was live action, whereas this is Thunderbirds-style "Supermarionation".  Also, UFO lacks the superhero-like protagonist we have here: due to his encounters with the Mysterons, Captain Scarlet can recover from pretty much any injury.

There's also the fact that this - despite its more "kiddie" format - is actually a considerably darker show.  In UFO, the aliens' motives for threatening us are unknown, and at the end of each episode their hostile intentions are thwarted by SHADO.  In Captain Scarlet, the Mysterons' hostility stems from the fact that we made a panicked and unprovoked attack upon them.  And while Spectrum often wins the day, the Mysterons do sometimes win a partial or even complete success in their schemes.  You don't often see a kids' show where the bad guys successfully carry out an assassination!

Unfortunately, despite its refreshingly 'grown-up' elements and the inevitable cool model designs that you'll see in any Anderson-led show, Captain Scarlet and the Mysterons suffers from two significant issues that prevent me from recommending it.  The first of these is that it lacks any kind of satisfying conclusion: in fact the very last episode is a clip show, while the second last is revealed to all be a dream at the end!

The other major issue is the writing.  Leaving aside that the Mysterons' demonstrable technological advantage is such that they could smash us like bugs whenever they wanted - we could perhaps excuse this by saying that they are deliberately drawing out the process of destroying us as a means of punishment - there's just some sloppy work here from time to time.  Like, you know, after 20 episodes of the Mysterons killing people and then replacing them with evil duplicates, your characters probably shouldn't be shocked when they find the dead body of someone they just saw in a seemingly hale and hearty condition.  And if you have the Mysterons say that there plans rely on capturing someone alive, they should probably not have tried to murder that person in a prior scene of the same episode.

If you grew up with Captain Scarlet and the Mysterons, I could see buying and enjoying it for the nostalgia factor.  Otherwise you should probably skip it.

I should note that there is a more recent (2005) CGI version of the show, which at the very least addresses the "doesn't have a proper ending" issue.  I may pick it up someday and see if the writing in general is any better.