The world of “Constantine” is a complicated one, combining elements of Catholicism, philosophy, theology and good ol’ comic-book horror. Our guide through this complex system is Keanu Reeves, who demonstrated in the “Matrix” films that, if nothing else, he can shut up and let the bizarre movie around him speak for itself.

“Constantine,” stylishly shot by music video director Francis Lawrence (with a nod also due to cinematographer Philippe Rousselot), is a good enough movie to make you forget, most of the time, how truly dreadful Reeves’ stilted, monotonous delivery is. There is a lot of talking here, often about things we don’t quite understand because the movie hasn’t explained all the rules yet, but most of it is done by the other characters, not Reeves.

Reeves plays John Constantine, a freelance exorcist who has a special connection to hell, having spent a few moments there during a near-death experience. Now, dying of lung cancer, he knows for reasons I won’t spoil for you that when he draws his last gasping breath, he will be delivered to hell permanently.

In the meantime, he roams the streets of Los Angeles — where else could a film about Heaven vs. Hell be set but the City of Angels? — maintaining the balance. You see, demons and angels are not allowed to come to our plane; they can only influence the people here. There are people called half-breeds, though, who are part human and part demon or angel, and who are therefore more susceptible to influence by their respective supernatural forces. This keeps things balanced. When a demon breaks the rules and actually crosses over into our world — usually in the form of a possession, a la “The Exorcist” — John “deports” that sucker back to hell, where he belongs.

John meets an LAPD detective named Angela (Rachel Weisz) whose mentally ill twin sister has just died, an apparent suicide, though Angela is skeptical. This ties in somehow with an unusually high rate of demon sightings that John has had lately, as well as with something called the Spear of Destiny that holds magic powers and was recently unearthed by a Gollum-ish Mexican boy. Some dusty old prophecies indicate all of this is a sign that Mammon, the son of Satan, is about to take over the world. This prospect is problematic for a lot of people, as you might imagine, so John must, you know, save the world and stuff.

John is aided by a few people, who no doubt support his mission more than they support him, since he is sullen and moody (though, in fairness, no more so than these reluctant-hero types usually are). Chas (Shia LaBeouf), whom John calls his apprentice but who is mostly his chauffeur, and Beeman (Max Baker), a geek who lives in a bowling alley and assists John with weapons and general nerdery, both provide some comic relief amid the brief sojourns to hell and the end-of-days mayhem.

There is also Gabriel (Tilda Swinton), a half-angel woman who advises John on occasion; her counterpart is Balthazar (Gavin Rossdale), a fey, nattily dressed half-demon.

I freely confess that there were several times in the film when I had no idea what was going on, so thick is the mythology surrounding John Constantine’s world, and so intermittently does the screenplay (by Kevin Brodbin and Frank Cappello) spell it out. But I generally enjoyed myself anyway, finding many of the theological ideas thought-provoking and much of the action butt-kicking. It’s a pretty respectable Good vs. Evil action thriller, filling its minutes not just with relentless adventure, but with stories and ideas, too, and always looking cool while it does it.

B (2 hrs., 1 min.; R, one F-word, some strong sci-fi violence.)