Factual error: Federal institutions have strict rules for inmates or patients based on the reason for their incarceration, including substituting metal utensils with safer plastic ones. Despite being convicted of brutally killing his family, Myers is still trusted with a sharp metal fork - resulting in the nurse's death.
Other mistake: In the original ending, after Laurie is pulled out of the cop car, Loomis is able to reason with Michael to let her go. After he does, he is shot to death by the police. This was obviously changed, but when Loomis is reasoning with him in the final cut, you can still see the police standing behind him. (01:46:00)
Plot hole: Laurie calls the police from 1987 Winchester drive, and gives them that address. Yet the police responding to the call go directly to 1960 Winchester drive - where Laurie has run to and is now hiding - even though it's on the other side of the street and several houses down. (01:31:30 - 01:33:40)
Factual error: When Laurie, Annie, and Lynda are walking home from school on Oct 31st, you see the "fall" leaves on the ground, however the surrounding trees are as green as can be. (01:04:15 - 01:05:30)