Close Encounters of the Third Kind (1977)
The story of a regular guy whose life dramatically changes after an encounter with a UFO was something Steven Spielberg had been trying to get off the ground for years. With the success of Jaws, the director finally had enough clout to make the film the way he wanted. Starring Richard Dreyfuss, Teri Garr, Melinda Dillon and French director Francois Truffaut in a rare acting role, Close Encounters was an unusual UFO movie because its kind, benevolent aliens weren't out to kill any earthlings!
Why 3D? The early scenes of a lost ship found in the middle of the Gobi Desert and a little boy watching as all of his toys start operating on their own would be even more fun to watch in 3D, not to mention Richard Dreyfuss' dramatic quest to find the mountain depicted in his mashed potato vision and, of course, the incredible alien spaceship in all its glory.