(at around 12 mins) The newspaper clip shown during the opening credits, which states that Laurie Strode died in a car accident, says that she was a survivor of the "Halloween murders" of 1968. They took place in 1978.
(at around 39 mins) In the classroom on the blackboard, the spelling of W.B. Yeats' name changes from the (wrong) spelling "Yates" to the correct "Yeats."
(at around 12 mins) In one of the newspaper clippings, Michael's last name is spelled "Meyers".
(at around 48 mins) When two of the characters are watching Scream 2 (1997) on TV, the movie skips about 5 to 10 minutes in 5 seconds.
(at around 54 mins) Laurie removes the top from a vodka bottle, guzzles, hands the bottle to Will who also takes the top off.
(at around 7 mins) An ice skate through the face would not be a clean stab, it would shatter the skull.
A picture at the beginning of the movie identifies Laurie Strode as graduate of the "Class of 1978." The original Halloween takes place in 1978., which means Laurie would have been a graduate in the spring of 1979.
The original movie has dialogue suggesting that it is Friday--in actuality, Halloween 1978 was a Tuesday. This movie also suggests that it takes place on a Friday, but Halloween of 1998 was actually a Saturday.
Officers respond to the burglary at Marion's house with the overhead lights activated on their patrol car. Officers would not normally respond in this fashion, as they tend to use a stealth approach not to announce themselves.
(at around 1h 13 mins) Laurie drops a knife after stabbing Michael, but a moment later a knife is still in his chest. She had two knives.
While the porch light of Nurse Marion's home is broken, the electricity is not off when Jimmy goes in; Michael cuts the electricity after Jimmy leaves.
The police investigation at the start of the movie is never mentioned again, but it was in a different jurisdiction.
(at around 1h 10 mins) When Michael hangs from the pipe at the school, Laurie's wound is visible before he stabs her.
At approximately 28 mins in Laurie gets out of her car and looks across the road to see some kids in costume and one little girl in a clown costume just like Michael wore, the same kids and the little girl immediately run by her on her side.
(at around 1h 16 mins) When Laurie is driving the van with "Michael" in it, notice in the long shots the road is solid pavement or concrete, a very "beaten path," however inside the van if you look outside the back window you can see the road is in excellent condition and has the yellow stripe down the middle separating the lanes.
(at around 1h 25 mins) Donald Pleasence's name is misspelled at the end of the credits when it says "In Memory of Donald Pleasance".
Scream 2 is playing in the background in one of the scenes. However, the original Scream had the first Halloween playing in one of its scenes, thus effectively negating the universe the Halloween movies take place in.
Laurie is having lunch in town with Will while she is on duty during school hours, and could have gotten into trouble for having wine with her meal.
In Loomis' office, there is a high school senior picture of Laurie saying "Class of '78". Halloween (1978) takes place in 1978 and Laurie is clearly seen leaving school while talking about textbooks, while in this film she specifically states she was 17 at the time her brother attacked. Either Laurie graduated a year early and decided to continue attending high school classes that fall, or more likely it was an error on this film's art department.
In the opening scene, a woman holds up a knife before she stabs it into a pumpkin. There's a sound effect of the knife coming out of its holder, however, the knife is in the air the whole time.
(at around 1h 8 mins) When Laurie, John and Molly are running away from Michael to the car, John is pushed into the back seat, when the door is closed, a very bright stage light is reflected into the window.
It's never really explained how Michael located Marion after 20 years since the events of Halloween and Halloween II, nor does it explain how he didn't locate her sooner.
Claudia's vehicle, which was stolen by Michael from the rest area, had a distinct body style. Since she and her daughter were neither attacked nor killed by Michael, she would have undoubtedly reported the car as being stolen, and it would have stood out to any officer seeing it along the way.
Michael's first scene in the movie shows him wearing the mask, but it's never disclosed where he got it.
With a mother as over-protective and skittish as Keri/ Laurie is, it is highly irregular that she wouldn't personally observe the buses departing for Yosemite and, therefore, see that her son was absent. She is also headmistress of the school and would likely be missed.