Let’s start with the bear attack, because it’s one of the most amazing spectacles of the movie year 2015. On its own, it’s reason enough to see “The Revenant,” and there are plenty of other reasons. For weeks, there have been rumors that the scene shows Leonardo DiCaprio getting sexually assaulted by a bear. That does not happen. What happens is even worse.

DiCaprio plays a fur trapper, in 1820, out in the Northwest wilderness, who thinks it might be a good idea to shoot a couple of bear cubs. He doesn’t notice the enormous mama bear running up behind him, until he turns around just as he’s getting pounced on. What follows is a scene that delivers in a number of extreme and wonderfully conflicting ways.

It is harrowing. It is technically remarkable, because there is no doubt in any viewer’s mind that DiCaprio really does have a bear throwing him around and stepping on his head. It is a beautiful piece of bear-fight choreography — it’s clear that serious thought went into how this fight would progress for maximum impact.

There’s also just enough emotional distance for us to enjoy what’s happening. The bear, after all, does have a point. And this distance allows us to notice and experience the scene’s other great pleasure: It’s funny. Bears are so cute and cuddly that to see one go berserk on a guy, particularly one who has it coming, has a certain absurd satisfaction.

“The Revenant” is loosely based on the real story of Hugh Glass, an American fur trapper who was abandoned by his companions following the unfortunate bear incident, and left to die. Despite infections and festering flesh, he somehow survived and navigated his way across 200 miles of hostile wilderness. It’s an amazing survival tale, and the movie itself looks like a survival chronicle. That really is DiCaprio with ice stuck in his beard. That really is DiCaprio wading and immersing himself in freezing water, over and over. Part of the pleasure of “The Revenant” is in watching freezing people from a warm cushy seat in a theater.

THE film is directed by Alejandro Inarritu in a Terrence Malick (“The New World”) vein, with shots of the sky through the trees, silhouettes against the setting sun and omniscient overviews of the entire landscape. The difference is that with Inarritu these are not occasions for philosophical contemplation. Instead, the sky might have arrows flying through it, signaling a new phase in an Indian battle. And the overviews, usually with some lone antlike figure in the midst of it, are there to remind you that this environment may be breathtaking, but people don’t belong here.

Like “Birdman,” and even more than “Birdman,” “The Revenant” is a director’s movie, a showcase for a filmmaker’s vision and innovation. Inarritu employs long, complicated shots that make full use of the wide screen. Early in the movie, he films an Indian attack in ways that make you realize that every previous director has done it all wrong. The attack comes without warning, from all sides. A character starts calmly barking out orders and is killed midsentence. Every moment is a horrible surprise, which, of course, it would be. There is no safe place to look, no safe character to follow.

Even a great innovator, though, has his limits, and in attempting to make an endlessly riveting film about a guy trying to crawl and limp for 200 miles, Inarritu has given himself a daunting assignment. He succeeds, in the sense that his 156-minute movie maintains interest, but the interest is maintained through a series of escalating catastrophes — Glass can’t just go over one waterfall, but several —and stock action-movie situations, such as the lust for revenge. The fresh brilliance of the first hour fades into something more familiar.

Tom Hardy exudes an awesome perversity as Glass’ most villainous colleague, but he probably would be more effective if he got past the idea that doing an American accent means talking like there are marbles in his mouth. Still, he’s a terrific presence.

DiCaprio doesn’t get to say much in “The Revenant,” but he does get to cauterize a neck wound with gunpowder (don’t try this at home), the most slapstick improvised health care procedure since Tom Hanks (“Cast Away”) extracted a tooth using an ice skate. And he does get to eat a live fish and dive face first into a buffalo liver. It’s hard to talk about this as a performance, because there’s nothing to compare it to. But if I were an Oscar voter, I might be tempted to vote DiCaprio best actor — or at least to propose a new category be inaugurated, the acting equivalent of the Purple Heart.