The Halloween 2007 ending leaves Laurie Strode's fate open: she and Michael fall over a railing, a gun fires, and the film cuts off as police sirens approach.
Here is how the last ten minutes work. Michael takes Laurie to his old house and shows her a photo of the two of them as children, and she stabs him in the neck and flees. Loomis arrives and shoots Michael, but Michael gets up, kills Loomis and drags Laurie back inside. In the final struggle on the upper floor they tumble over a balcony railing, Laurie ends up holding the gun, and it goes off as she screams. The picture ends there, with the sirens as the only answer.
What does that cut mean? In my opinion, it is the logical end of a film that gives its whole first act to how Michael was made. Zombie spends the opening on the bullied ten year old who makes masks, on the mother, and on the baby sister he spared. So the climax is not a stalker meeting a random victim. It is a brother trying to take his sister home, and the photo of the two of them as children is the emotional hinge of the scene. The gunshot, not a clean kill, is the right punctuation for that.
There was another version. A different ending was shot in which Loomis talks Michael into letting Laurie go before police shoot Michael dead, according to Wikipedia's account of the production. That cut resolves the story. The finished film does not, and that ambiguity is what leads into Halloween 2 2009, where Laurie has survived and lives with Sheriff Brackett and his daughter Annie, while Dr. Loomis has become a celebrity with his book about the events.
How does this compare with the rest of the series? The Halloween 1978 original also ends with Loomis firing on Michael, and Zombie reworks that beat by letting Michael rise and kill the doctor, a harsher turn for a character who spent the film trying to treat him. Halloween H20 and Halloween Resurrection go the other way: Laurie fakes her death and then faces Michael as a fully formed survivor. In 2007 she has barely begun that road. The 2018 film later lets Laurie spend forty years preparing for Michael, and by comparison Zombie's Laurie is unprepared and ends the film on the floor of his childhood home.
It could be argued that the open ending also fits the genre, since a monster who survives a stab to the neck and a gunshot is not going to stay down. For how this timeline sits beside the others, see Halloween timelines explained.