I saw this series when first aired, when I was just a kid, and while I remembered little about the story, I did remember that it made more of an impression on me than most SF shows of the time. Now I can see why.
The setting is very much 'future 70s', with hippies, oil restrictions, social collapse, power cuts, and other fears of that era, the effects are certainly very old by modern standards, and Mills' Quatermass is too undeveloped and unsympathetic for my tastes. However, the story makes up for it, and there are some memorable ideas (like gladiatorial games in Wembley Stadium) and some memorable scenes (again, the Wembley Stadium 'harvesting' scene in particular, and the S&M 'family show' would also have been a lot more fun on Saturday night TV than Noel Edmonds).
One thing I hate about bad SF is that the aliens are just people with a few rubber bits stuck on their face, who come to Earth to kidnap women or steal our resources, or some other mundane and, frankly, very human goal. Quatermass' aliens, on the other hand, are never seen and we never even really find out quite what they're doing, just that they're extremely powerful and don't care about humans in the least... it's a far more intelligent premise, and very Lovecraftian, in a way.
So, the effects are dated, Quatermass himself could have done with more work and possibly a different actor, but overall it's an intelligent premise, and, frankly, the idea of an attack by hugely powerful aliens who care nothing for the human race is far more scary to me than most so-called 'horror' movies of recent years.
