In fact, this movie has no purpose whatsoever. It says nothing, it accomplishes nothing, and it does nothing. It's a story for telling a story's sake. But where Inside Llewyn Davis (2013) tells a story because of the existence of the story, Cocoon must search out the material to make the story. And the screenplay looks long and hard for that inspiration for a good story – and gives up. So we get a movie with old people and aliens. A story where old people of Earth have more in common with aliens from some distant planet (that have apparently been to Earth already, explaining certain human legends) than with their own kind. But where E.T. the Extra-Terrestrial (1982) makes good use of moral children and friendly aliens, this movie decides to attempt to make a sentimental story with a stupid child and indulgent aliens. But wait there's more! Don't forget the necessary, underdeveloped, and makes-no-sense-whatsoever love story – in this case between a human and an alien.
The beginning was decent however. Howard attempts to construct a slowly building tense storyline of gradually revealed twists. Which works until it feels like the movie should end at around the 80 minute mark instead of the 120 minute mark. The slow sci-fi drama of the first half is quickly overshadowed by the feel-good catastrophe of the second half.
Don Ameche was decent, but I think the Academy has something for old people, like Art Carney in Harry and Tonto (1974). While good performances, do they deserve the Academy Award? The visual effects were good for the time and not abused unlike many an action and sci-fi movie of today, not to name names. If only Howard could have kept the slow build up going, like Arrival (2016), he would have had a fine classic entry into the 80s sci-fi movie collection. Now, we just have Cocoon, the classically bad movie.