“Bellflower” has earned a significant number of detractors since its premiere, and believe me, I get where they’re coming from. This is one odd, potentially off-putting movie. But if you see it, whether you love it or hate it, you won’t soon forget it, nor will you see anything like it for a long time.

Oh, it starts out ordinarily enough. Here are a couple of slacker guys, Woodrow (Evan Glodell) and Aiden (Tyler Dawson), who enjoy a state of arrested development in one of L.A.’s less glamorous neighborhoods. They are fixated on “Mad Max”-style post-apocalyptic scenarios, and to that end spend all their time building an indestructible car and constructing a flamethrower. If the apocalypse happens, they will be ready. If anything else happens — say, if they need to get a job, or pay some bills, or take on a responsibility — they will be quite a bit less ready.

Woodrow and Aiden’s friendship is momentarily disrupted by the appearance of Milly (Jessie Wiseman), a beautiful blonde with whom Woodrow begins a whirlwind romance. Milly is similarly free-spirited and bohemian, and likewise apparently unencumbered by employment. She and Woodrow are adorable together. He’s a little shy; she’s a little wacky. “Bellflower” seems to be shaping into a sweet, low-budget, mumblecore-influenced romantic comedy.

And then … wow. And then. After establishing a completely believable and lived-in relationship for Woodrow and Milly — one that rings true for all who have ever been young and smitten — the film just as capably shows the disintegration of such a relationship, the boredom and complacency that can emerge over time. We were hooked by their giddy romance, and now the rug is pulled out from under us. “Bellflower” has deftly transformed into an insightful drama.

And then … and then. Man. You’re not ready for this. When things go south with Woodrow and Milly, the movie evolves even further, and now it does not belong to a genre. There are elements of horror, exploitation, vengeance, tragedy, and buddy comedies. There is more fixation on post-apocalypse survival techniques. The timeline gets fractured. Unspeakable things occur.

Evan Glodell, who plays Woodrow, also wrote and directed the film. It’s his first feature. He even built the cameras he used to shoot it, for crying out loud. He’s some kind of mad genius, a techie nerd with leading-man good looks and the warped imagination of Chuck Palahniuk. He uses the film’s microscopic budget to his advantage: one minute we’re smiling at the charmingly unpolished sound editing and scratchy images, mentally patting Glodell on the head and saying, “Aw, what a cute little movie you’ve made!”; the next minute we’re shocked by some dark, clever turn and realize we’ve been played. Glodell knows exactly he’s doing.

We throw the word “daring” around too often, but that’s what “Bellflower” is. Glodell took incredible risks as a filmmaker, telling a completely unorthodox story in a wholly audacious manner. (He and the cast took physical risks, too. With no special-effects budget, those flamethrowers and other implements of “Jackass”-inspired destruction are real.) Even casting himself as Woodrow was gutsy, since the film lives or dies by our affection for that character. If the film had failed, it would have failed spectacularly.

As I mentioned at the top, there are some who believe the film did fail. I don’t begrudge them that opinion. Goodness knows something as brazenly unusual as this won’t be everyone’s cup of tea. Even if you “get” it, you might not like it. That’s fair enough. All I can do is report my experience with the film, which is as follows: I laughed, I gasped, I felt touched by the warmth, I felt disturbed by the madness, I marveled at how real it all seemed, and I haven’t been able to stop thinking about it.

A- (1 hr., 43 min.; R, abundant harsh profanity, some graphic violence, a couple scenes of nudity and strong sexuality.)