Whilst there are some visual and thematic similarities, they are, I think, very, very different films.

Close Encounters is emphatically a science fiction film about contact with another world on a much bigger scale, tying in to real life mysteries (Flight 19, etc). Roy has a very, very different narrative arc to Elliot. He essentially is driven mad to the point that he abandons his family, never to return, crossing into another world.

E.T., by contrast, is a fantasy film. A modern fairy tale about childhood innocence, imagination, about the pain of divorce, about the empowerment of children, and coming of age. It's also a love story, a fable about prejudice, a Christ allegory, the universal need for "home", and so much more besides. In the end, Elliot comes to understand how love and pain are inseparable, but he is stronger and wiser because of his experiences. Unlike Roy, he remains on Earth. It's a lovely film, and extremely different. A genre apart, I'd say.