How do you wrap up an alien invasion movie?
If you're a typical Hollywood director, you start with a grandiose speech about humanity surviving against all odds, then you engage in a fierce last stand battle, blow up a city's worth of buildings, and conclude with the hero walking triumphantly from the dust and rubble as his love interest leaps into his arms before they vacation in Hawaii. Assuming there's a Hawaii left to vacation in.
Or if you're Steven Spielberg, you put the kibosh on all that nonsense and invite the aliens over for an intergalactic jam session.
When You Wish Upon a Star
Don't you love happy endings?
In CE3K, almost everyone seems to get what they want by the end of the film. Jillian gets Barry back. The country gets its missing airmen and sailors back and those guys get to go home. Lacombe gets the answers he's been seeking all over the globe. Humanity gets an intergalactic lesson in communication and goodwill. The aliens get some fellow travelers. And Roy—well, we can't even.
The viewers get the lesson Steven Spielberg intended. As he told an interviewer in the TBS documentary Spielberg on Spielberg, "If we can talk to aliens in Close Encounters of the Third Kind, why not with the Reds in the Cold War?" (Source)
But what about Roy's wife and kids? Where's their happy ending? The director admitted that he probably left that hanging because he didn't understand families. He told Cinema Confidential, "Now, that was before I had kids. That was 1977. So I wrote that blithely. Today, I would never have the guy leaving his family and going on the mother ship" (Source).
He went on to say that he didn't make that same mistake in War of the Worlds, but his insight came too late for the Neary family.