Gerry Anderson's two seasons of Space:1999, and the prequel series UFO, seem to me to be three separate eras in one long story, rather like the eras of three different Dr.Whos, or perhaps different spin offs of Star Trek.
If that's the case, UFO is the equivalent of the Tom Baker era or the original Star Trek, it's the one that gets all the respect. Season 1 of 1999 is like the Davison era or perhaps Next Generation of Trek. Season Two of Space:1999 is like the Colin Baker era of Who, or Deep Space Nine in Trek. Yes, it is the one no one wants to admit they like, but if given closer examination with an open mind, it actually has much to offer and much to enjoy. This little lot contains some superb contributions by great writers. Terrance Feely (UFO, The Prisoner) delivers the goods in the excellent Bringers of Wonder, while Pip and Jane Baker (Dr.Who) write the low key but good A Matter of Balance. And then there's the superb Seed of Destruction, a compelling doppelganger story with an evil Koenig taking his place on Alpha. Space Warp, on the other hand, is written by Fred Freiberger and unlike the fun Beta Cloud, it sucks. Not to worry, though, the rest of the series is so much fun and so well produced that it is still totally entertaining and enjoyable. These characters are not as dark as the ones from the previous seasons, but they are fun and likeable enough to care about and enjoy their adventures. An underrated gem of a series!