Solaris. Either the original Russian of the George Cloony remake. The thing I liked most about the remake was they kept the slooooow pacing of the original. Doesn't feel like an American movie at all.
Thought-provoking in that it pointed out that no alien species is in any way obligated to be understandable by the likes of us, & resisted the annoying Hollywood urge to explain everything at the 3rd grader level. They never explained ANYTHING.