Not a classic, but they can't all be.
The original Halloween was a box office smash in large part because of the innovation of serial killing in the early '70s. Serial killing wasn't itself new... this was a phenomenon that dates back to at least the renaissance era. But the '70s were a perfect storm of influences that led to a wave of high-profile killings which would dominate news headlines. Violent imagery of the war in Vietnam, a cultural malaise brought on by economic stagflation, & the threat to white male dominance posed by civil rights & feminism all contribute the the emergence of now infamous killers like Ted Bundy, John Wayne Gacy, & David Berkowitz. Even lesser known killers got catchy monikers like "The Southland Strangler" or "The Casanova Killer." And America became accustomed to tales of violence & cruelty. The only real difference between a film like Halloween & the news coverage of the time is that it simply showed what reporters were only describing or alluding to. And audiences turned up to see this in droves.
John Carpenter has credited the Mask of Sanity, a breakthrough work in the study of psychopathy by Dr. Hervey M. Cleckley, for shaping the character of Michael Myers. And it's that interpretation of the sensationalist headlines through an earnest attempt to understand the mind of the killer that provides the DNA for the such a compelling film. Only filmmakers who attempted to capitalize on Halloween's success would not treat their characters with the same degree of nuance.
Within a year after Halloween's release, copycat films like Friday the 13th were already playing in theaters, & a wave of other slasher flicks were quick to follow. Only they copied the relatable teenage characters, the menacing point-of-view camera angles, the foreboding soundtrack, & the brutal kills, but left behind the character development, pacing, & overall restraint that made the original Halloween so special. Instead, they relied on disposable characters & increasingly brutal death scenes, wagering that you can make up for character development by substituting more blood & guts. And they were right. At some point contempt for the characters breeds just as much a reaction as compassion, so long as you pay it off with a gory enough kill. And the copycat films leaned hard into this calculation.
Consequently, a phenomenon developed where each successive slasher film had to have more, bloodier deaths than the last in order to achieve commercial success. And the Halloween franchise was not unaffected by the corn syrup arms race.
Studio pressure & Carpenter's own insecurities led to a sequel script that was far more gratuitous than the original, & a host of hospital workers are introduced ostensibly for Michael to slash his way through on his way to finishing what he'd started with Laurie, who is recovering from the nights earlier events. One particularly gruesome scene involves a naked nurse whose face is melted in a boiling hydrotherapy pool. Which isn't on its own a bad choice, but the context is such that the audience wants to see her naked & wants to see her killed. And this objectification of the character is a deviation from the spirit of the original film.
One gets the sense that Carpenter has a growing contempt for what his original film hath wrought--a demand for onscreen violence as an end unto itself--& so he's making a sincere attempt to addresses any lingering plot questions in the screenplay. He explains that Michael is hunting Laurie because she's his sister & that he's trying to make ritual sacrifices for the Celtic holiday Samhain. And he then blows Michael & Dr. Loomis to smithereens in the final scene. Carpenter later remarked that certain aspects of his own screenplay were "just awful," & director Rick Rosenthal fought a losing battle against him over what he felt were unnecessarily goory inclusions for the sake of commercial appeal. But the cat & mouse sequence makes the movie worth watching, despite its many shortcomings.
Ultimately, Halloween II is a film that lacks inspiration. Carpenter participated mainly because he felt he was undercompensated for the massive success of the original film, & Jamie Lee Curtis returned mostly out of a sense of obligation to Carpenter, who provided her big break. In fact, she wears a terrible wig throughout the film after having cut her hair for another role. And in the end that wig may be the best metaphor for this sequel: recognizable, but unconvincing.