I was utterly rivetted by this film when I saw it in '77.  It had no shoot'em up alien stuff, but instead is an extremely subtle exploration of first open contact with alien explorers.  THere is a lot of humor and mystery in it, unexplained things that come together in the end in a wonderful and optimistic climax.  I found it a powerful emotional experience then, and seeing it nearly 30years later - with my kids, who were also fully engaged in the mystery and mood of it - equally satisfying (ok, a bit slow at time for them as they are used to star wars action and pace).  Indeed, this is one of the best sci-fi films I have ever seen.