Factual error: Unbelievable that for 30 years no one has pointed out that in every shot with the moon, except when the moon is full, the crescent is pointing the wrong direction. In the evening (ordering pizza), in the Northern Hemisphere (California), a crescent moon will always be pointing down to your right (the bright side will be on the lower right). The only time it could point the way it does in these scenes is in the wee hours of the morning, at 4 or 5 a.m. and looking to the East. Spielberg didn't even fix it in the re-release.
Suggested correction: Actually the problem with moon scenes that we see a crescending moonphase (less than a quarter) when Elliott first meet E.T. After that in a couple of days there is a full moon which could be reached in about 16-17 days from that phase which we saw first. It would be also about 11 days if the first shot was mirrored and actually was an increasing moonphase. But the whole story is about 6 days long. So a full moon couldn't be reached from a quarter of moon.
Other mistake: Whatever E.T. feels or things happen to him, Elliot experiences them too, but when Mary takes a photo on Halloween, only he faints and Elliot doesn't, despite their mental link.
Suggested correction: E.T. doesn't faint. He is just startled and stumbles and falls over backwards.
Continuity mistake: When Elliot shows up the morning after Halloween her mum hugs him and gets dark paint on her cheek. When the angle changes the stain vanishes.
Suggested correction: Mary doesn't get "dark paint" on her cheek when she hugs Elliot. When Mary's standing at the fridge door speaking to the police officer, she's still wearing her Halloween dress and the mark on her right cheek is the black heart (part of her Halloween makeup). This mark is still visible on her cheek in the wide shot (viewed on Blu-ray) when she tells Elliot she's sorry that she yelled at him, and sits Elliott down on the kitchen seat.