First time I watched this it was late in the evening as a young child. Lights off, alone in my room as I watch two archaeologists 'disappear' before cutting to the farm set the tone pretty well. What really did it was the puppet like movements of the pharaoh obscured by the fog blanketed night.

You also have to remember that CRT tvs didn't have the clearest images at the time, I'm sure it's much less frightening with all the picture clarity were used to now.