Don't know about the States, but across the pond from there, THX 1138 is not as well known as it probably deserves. I hope the public here can appreciate this Sci-Fi movie and Duvall is great there.

https://en.wikipedia.org/wiki/THX_1138

It's known over here (to the degree that it is at all) for being the source of the THX name that Lucas later used for his digital sound system. But the movie is interesting in itself as an early pre-fame Lucas movie.