I remember seeing that when I was a kid in the early 80's. In those days you could get a lot of video nasties from the rental shops as they hadn't yet been banned! The Sentinel was definitely one that stuck in my mind, more so than a lot of the gorefest ones.
The original Hills have Eyes was quite creepy and also I think we should mention Poltergeist, Rosemary's Baby and The Shining which are pretty good scary films.