I'm not saying I wanted every little question answered, but as-is the aliens seem like complete assholes. Kidnapping people from their own time and returning them to the planet several decades later is probably a fate worse than death; all your friends and family are dead or dying and the culture shock would drive you insane. Now, had there been an unintentional reason why the aliens committed these kidnappings, I would have been properly distracted.
On second thought, they're fuckin' aliens. Why the hell should we understand what they're up to?
There are two plots running in tandem until they inevitably cross paths near the end: in one, Francois Truffaut and Bob Balaban play a couple of G-men globetrotting from one mystery to the next. In the other, middle class electrician Richard Dreyfuss is driven mad following a late night UFO sighting. Teri Garr is alienated by her husband's newfound eccentricities, which leads to him losing his job and a mental breakdown for her. Dreyfuss only finds an ally in the form of Melinda Dillon, a single mother whose three year old seems to have a unique connection with the visitors.
So you have two duos racing to reveal the truth from completely different angles. Most movies don't have one interesting duo (Exhibit A: any action-comedy film coming out this season), much less two, and the fact Truffaut and Balaban aren't the emotionless agents seen in almost every other alien movie makes this one all the more special. It's curious the two men have to overcome their language barrier, which they'll do again with the aliens themselves.
My favorite thing about this movie is Truffaut, who feels like an accidental brushstroke in just the right place. How did Spielberg know the guy could act? What made him think Truffaut would work out at all, much less so brilliantly? Why the hell didn't Truffaut act in more movies?
If it isn't clear at this point, Close Encounters is one of my favorite Spielberg movies. I think it's the crowning achievement of his earlier career and the phrase "movie magic" was invented for stuff like this one (I would kill to see it at my local drive-in). It contains absolutely everything summer blockbusters forgot how to do in the twenty-first century.
If you've already seen the theatrical version, I think the Collector's Edition is where it's at. Sometimes it's hard to tell which version you're getting, but if the run-time is listed at 2 hours and 17 minutes, it's most likely the Collector's Edition. And even if you've never seen the movie, I still think the Collector's Edition is a good place to start.