I first saw this back in '79 and possibly because I was a lot younger then, I thought it was great. Having watched it again, it does come across as rather weak, particularly when comparing it to the old black and white classic "Night of the Demon". In the next paragraph there are going to be a couple of spoilers, so for those of you who haven't seen it and wish to, please skip the next paragraph.
For one thing, I couldn't understand why Carswell had to be 'American'. In the original film he certainly wasn't and I've heard various stories that his character was based on Aleister Crowley, who, strangely enough was ..... English!!!! Iain Cuthbertson is a great actor but why he was forced to put on an American accent is beyond me. The other thing I found quite ridiculous was the huge spider in the 'victim's' bed. Again, referring back to the old black and white film, the experiences that the victim had were more 'suggestive' rather than obvious. The final thing that I found a total contradiction - when Carswell goes to the desk at the airport terminal he has no idea that his victim takes the place of one of the other assistants. He knew well in advance about her coming to his house (as his housekeeper announced "Mr Carswell has been expecting you", but had no idea she would be at the airport. Surely an inconsistency here?
I think the whole plot, and again I apologise for making constant comparisons between this version and the original "Night of the Demon" film, was weak and didn't keep you gripped in suspense. There's a lot to be said for these old black and white classics - if I had to make a choice between seeing this version again and "NOTD", I know which one I'd opt for! Good old Dana Andrews - you show 'em how it should be done!!!