Overrated and boring
I've tried to watch this movie three times and failed on every occasion to derive any enjoyment from it.
Its main problem is the lead actress, Cristina Raines. She's just not good enough as an actress to carry this movie as the lead. She is so dull and basically you (I) don't care about her, or what happens to her in the film.
Even a star studded cast including Burgess Meredith, John Carradine, José Ferrer, Jeff Goldblum, etc, can't rescue this boring film. The characters are dumb and over the top ridiculous.
The Sentinel has be compared to Rosemary's Baby (1968). That's just a plain insult.