I was born a little too late to see Space: 1999 when it originally aired, but I saw models, still shots and comic books from the show as a young 'un and thought it looked awesome. Mostly because at that age I thought anything with spaceship was cool, and it had some particularly neat-looking ones. Alas, when the show finally became available on DVD, I was rather disappointed: its efforts to be cerebral were mostly just boring.
All of which is relevant to this review mainly because Space: 1999 was the show born out of the decision not to proceed with UFO: 1999, which would have been a direct sequel to UFO, set approximately 20 years later. Many of the sets for the cancelled show had already been built and creator Gerry Anderson (of Thunderbirds fame) simply re-purposed them.
The concept of UFO is that in 1970 the governments of the Earth get incontrovertible proof that aliens are visiting our planet to kill or abduct human beings. Over the next ten years they establish a secret organisation - SHADO (pronounced "shadow") - to fight the alien menace. SHADO's resources include a moon base, a trio of space interceptors, and submarines capable of launching aircraft ... as well as some of the goofiest uniforms you have ever seen.
Alas, those early episodes are definitely the best part of the show: those later in the production schedule tend to suffer from the same not-as-clever-as-they-think-they-are script issues that would later plague Space: 1999. Also, given that this show was not intended to progress beyond the 26 episodes here, it lacks any real sense of development or conclusion (the show was beset with production problems, which may have contributed to this).
Overall, on the strength of its gonzo costuming, intriguing - if wholly inaccurate - vision of the 'future', and strong early episodes, I'm going to give UFO a qualified recommendation. If you're a science fiction fan, it's worth a look.