Ignore - Halloween III: Season of the Witch, Halloween 4: The Return of Michael Myers, Halloween 5: The Revenge of Michael Myers, Halloween: The Curse Of Michael Myers, Halloween Resurrection
There are a lot of problems with this series. The continuity of the story veers all over the place from strange men in black, to old fashioned crazy curses, it's rather annoying that the original, often praised due to it's simplicity, would spawn such a mess of a mythology that seems to makes almost enough sense to function, but then not really if you have a proper look at it.
If you only consider the first two and then the sequel that brought back Jamie Lee Curtis, then the film makes a rather neat trilogy, that gets rid of some of the more insane cultist behavior that later installments would display.
After brutally murdering his older sister when he was six years old, Michael Myers escapes from the mental asylum he has been locked in and comes back to town to kill teenagers, with his goal seeming to be the murder of Laurie Strode. The first two films deal with his rampage in Haddonfield over the night of Halloween 1978. It's revealed that he wants to kill Laurie Strode, due to the fact that she is his sister and Michael seems to really like killing those related to him.
After a final showdown in a hospital, Michael and Dr. Loomis are seemingly incinerated in a fire at a hospital, which seems to have finally stopped the masked killer.
Now, just forget the other dreadful films exist, especially Season of the Witch, a film even the producers want to forget about and move straight on to H20: 20 Years Later
Twenty years later, Laurie has assumed a different identity after faking her death and has become a headmistress in a private school. No evidence of Michael was found in the hospital and Dr. Loomis became a recluse due to his ill health and spent the rest of his life trying to find a way to stop Michael should he return.
Michael finds out where Laurie is and tries to finish the job by tracking her down. He begins another rampage and Laurie emerges victorious, after stabbing him and watching him fall from a great height.
He is take away on a stretcher, though Laurie is convinced that he will return from the grave again, so she steals the ambulance and takes it out to an abandoned part of the forest where, sure enough Michael rises from the gurney. Laurie wanting to end this once and for all, crashes the car and ends up pinning Michael to a tree.
Then comes the pivotal moment, where she realizes that despite the fact he's a homicidal maniac, he is still her brother. In a moment of possible reconciliation she realizes that Michael is batshit crazy and takes his head off with a fucking axe. She lets out a sigh of relief. Her nightmare finally over. Cue the credits on the trilogy.
Forget the absolutely ridiculous explanation of her actually killing a paramedic with a crushed larynx in the follow-up and you have, dare I say it, an excellent horror film trilogy.