Horror movie fans know that normally the terrors they savor lurk in the dark; not long ago David F. Sandberg used the topos as the basis for “Lights Out,” effectively winking at the audience in the process. In “Midsommar,” writer-director Ari Aster deliberately confounds expectations: the bulk of the film is set in northern Sweden in June, when the sun never sets. The chills it endeavors to generate will, except for interior shots, occur in brightness so intense as to be almost blinding.

While one can appreciate his desire to do something different, however, this follow-up to Aster’s “Hereditary,” one of the best genre pieces of recent memory, turns out to be ambitious but predictable, moody but sluggish, only sporadically creepy and sometimes deliberately repulsive, and, ultimately, rather dull.

In any event, “Midsommar” isn’t quite different enough: its premise, deriving from the idea that pagan elements in traditional fertility rites can have dire consequences, hearkens back to “The Wicker Man,” both Robin Hardy’s 1973 cult classic and Neil LaBute’s misguided 2006 remake. There are differences, of course: a Scottish isle was the locale in the original “Man” (changed to one off the Pacific Northwest coast in 2006), and the outsiders in this case are a group of grad students, not a lone policeman. But though Aster adds other themes to the plot to replace the “procedural” underpinning of Anthony Shaffer’s script, an air of familiarity hangs over the film.

The students are a trio of friends—Christian (Jack Raynor), Josh (William Jackson Harper) and Mark (Will Poulter). The first two are apparently anthropology majors working on their theses—Josh more advanced in the process, Christian still dithering over a topic. Mark, by contrast, is just a hard-drinking lout with a sexist streak; his object of study seems to be women. They’ve all been invited by their soft-spoken Swedish classmate Pelle (Vilhelm Blomgren) to attend the midsommar festivities that his home community holds each year.

They will not be going alone, however. Christian’s girlfriend Dani (Florence Pugh), a psychology student, decides to tag along. She’s in a terribly fragile state, having just lost both of her parents and her mentally troubled sister in a single horrible act of murder-suicide; and Mark has advised Christian to dump her as too high-maintenance. But, as with his thesis, Christian vacillates, though he’s unwilling or unable to give her the emotional support she so desperately needs.

When the group reaches the remote community, a gaggle of white-robed adherents presided over by an officious though welcoming matriarch called Siv (Gunnel Fred), they find that Pelle’s “cousin” Ulf (Henrik Norlen) has brought another outsider couple—Simon (Archie Madekwe) and Connie (Ellora Torchia)—to the ceremonies. All become part of the curious communal practices, which include elaborate outdoor meals, maypole dances and, as gradually becomes apparent, consumption of hallucinatory drugs and extremely strange traditions, some even odder than placing their record-keeping in the hands of oracles disfigured by the fact that they are products of incest, such as ritual sacrifices designed to ensure the community’s prosperous continuance. The caged bear nobody discusses will, of course, prove an element in one of these.

Josh and Christian are fascinated, if occasionally revolted, by what they witness, both deciding to make the community the focus of their research—which causes a rift between them that leads to violence (as does Mark’s violation of community norms). By far the greatest chasm, however, is the one that deepens between Christian and Dani. She, with her longing for family, is drawn into the community to an all-encompassing degree, while he is seduced by a beautiful maiden into an act of betrayal that turns out very differently from what he expected.

To give “Midsommar” its due, the film is visually remarkable. Henrik Svensson’s production design—with its surrealistically shape buildings set against the green fields and towering rocky cliffs (the film was actually shot in Hungary, not Sweden)—and Andrea Flesch’s liturgical-style costumes blend into an evocatively sinister whole. Cinematographer Pawel Pogorzelski captures everything in images of surpassing beauty, the languid pans contributing to Aster’s vision. The same is true of editor Lucian Johnston’s ultra-deliberate pacing.

The difficulty lies in that vision. In “Hereditary” Aster embedded the story of a family’s disintegration within the context of a horror plot about cultism and succeeded almost completely, a misjudged ending apart. Here he connects a tale of a relationship’s collapse to another cult’s scheming, but with significantly less success. While “Hereditary” was brooding, it also had vigor, and its periodic shocks were measured rather than disgusting. By contrast “Midsommar” is so enamored of its woozy style that it plods, and resorts too often to scenes that are designed to repel. Aster obviously intends to ratchet up the tension slowly before his big, shocking revelation; but this time around the pacing seems merely dilatory, and the closing twist something that most viewers will have foreseen far in advance.

One thing the two films do have in common is exceptional performances by the female leads. Toni Collette was amazing in “Hereditary,” and Pugh is very fine here, capturing Dani’s on-the-edge psychological state well, even if her transformation in the film’s later stages has to be intuited rather than felt. But Collette was matched by the equally remarkable Alex Wolff, playing her son, who was as much of a target as Christian proves here. Raynor is far less compelling, and though the essential weakness of his character helps to explain why, it creates imbalance in the script’s main thread.

Apart from Dani and Christian, moreover, Aster treats his characters perfunctorily, barely sketching their personalities with a sort of cinematic shorthand (Poulson’s Mark is a particular case in point), and the actors respond with lackluster performances. Aster doesn’t help by coasting over major plot points without explanation—some deaths occur off-screen, hardly remarked on—and most viewers will probably find the big finale more ludicrous than satisfying, especially after waiting two-and-a-half hours to get there.

One shouldn’t write off Ari Aster: he has a distinctive voice, and the skill to express it in striking cinematic terms. But here his considerable talents are weighed down by a need to appear a profound artist, and the outcome is a film that, like Luca Guadagnino’s recent remake of “Suspiria,” winds up as a lugubrious exercise in self-indulgence. But many filmmakers have recovered from the sophomore curse, and he can recoup; he needn’t go the way of, for example, Richard Kelly.