I saw it when it was shown on TV in 1981. I was 10, and a friend was staying over as his parents were on a work trip (they were very genteel art historians, and the idea would probably have given them a heart attack). We were assumed to be asleep in the spare room, but had hatched a plan to watch it, presumably with the sound turned down very low.

I mainly remember being traumatised by the [mild spoiler] pane of glass on the back of the truck scene, for years.

I think it might have put me off the idea of horror movies, until I got into the camp Hammer stuff a few years later. But proper, actually meant to scare you horror has never really appealed, perhaps because of that unwise rebellious viewing decision at the age of 10.