There are a number of theories about what has the most impact on a movie. Is it the script, the director, the budget, the effects?

I always had leaned toward the screenplay, until this year when a pair of similar movies changed my mind: the biopics “Ray” and “Beyond the Sea.” Both were written like a TV movie of the week and prone to thematic missteps. The difference was “Ray” had a perfectly cast Jamie Foxx in the lead role and “Sea” had a way-wrong-for-the-part Kevin Spacey.

“Ray” went on to earn six Oscar nominations. “Sea” drowned in bad reviews and was ignored by audiences

Now casting has creeped to the top of that debated list.

Maybe that’s why “Constantine,” the latest comic-book adaptation, is so effective at rising above its source material. The cast is comprised of a quirky, unpredictable group of character actors that can’t help but put a fresh face on the same type of supernatural-action tale that’s resulted in tepid adaptations such as “Hellboy” and “Spawn.”

(It’s sad how the casting directors never get any recognition.)

The movie is worth a look just to see British actress Tilda Swinton (“The Deep End”) play the archangel Gabriel or stoic Swede Peter Stormare (“Fargo”) portraying Satan like an effeminate drug kingpin. Even Bush singer Gavin Rossdale makes an impression as an impeccably dressed demon named Balthazar.

And who could forget headliner Keanu Reeves? Usually I can — especially when it comes to the collect-the-paycheck turn he gave in the abysmal “The Matrix Revolutions.” But the brooding Reeves is far more dynamic in this thriller than his last dozen or so movies. It’s his best performance since 1997’s “The Devil’s Advocate,” which also placed him onscreen opposite Lucifer.

If “Angel Heart” is ever remade he might want to consider taking the role.

Keanu Reeves plays John Constantine, a paranormal investigator trying to prevent forces of the underworld from roaming the earth, in Constantine, which opens today in Lawrence.

Reeves plays John Constantine, a paranormal investigator who often partners up with the Catholic church to carry out exorcisms and prevent underworld minions from mingling with humans. You know, the usual send-demons-back-to-hell gig.

But time is running out for the man. Incessant chain-smoking since he was 15 has left him with lung cancer. And since he committed suicide as a youth but was “resurrected,” he knows this sin ensures him a reservation with the damned when he permanently dies. The proposition haunts him because, “How’d you like to be sentenced to a prison where half the inmates were put there by you?”

For Constantine’s latest job he teams with a police detective (Rachel Weisz) whose twin sister apparently committed suicide. She believes her sibling would never have done such an act, and that there are dark forces at work … even darker than normal. Then when demons begin walking the streets of Los Angeles, Constantine realizes the normal balance in power has somehow shifted.

“We’re finger puppets to them, not doorways,” he says.

Based on the DC/Vertigo comic book Hellblazer (the title was changed so as not to be confused with “Hellboy” or “Hellraiser”), “Constantine” never delivers a story that is all that compelling. Yet it manages to create characters who are worth the attention.

Constantine himself walks the cynical, aloof territory of most modern noir heroes. But his skills are more interesting — specifically, his ability to re-enter hell when needed. This requires a peculiar method of “astral traveling” involving a pale of water and a cat.

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Rookie director Francis Lawrence, a former music video veteran, paints a rather visionary picture of Hades. It’s depicted more like a city that has suffered the aftermath of a nuclear attack … with ravenous demons.

This is one of many piercing visuals that do a fine job of creating the off-balance, odd-angled world of modern comic books. Lawrence handles these tricks well without overly relying on them. He also proves better at juggling the neo-religious elements central to the story far better than, say, the last two “Matrix” films. Suddenly, Reeves doesn’t seem so ridiculous.

But even though the casting is inspired (throw in turns by Pruitt Taylor Vince as a overworked priest and Djimon Hounsou as an omnipotent witch doctor named Midnite), not every choice pays off. “Holes” star Shia LaBeouf portrays Reeves’ youthful assistant, Chas, in a role that could kindly be called extraneous.

Rachel Weisz and Keanu Reeves team to discover the secret behind a suicide victim in the supernatural thriller Constantine.

“You’re not a slave,” he tells the kid. “You’re a very appreciated apprentice — like Tonto or Robin.”

I think of him more like Incredi-Boy from The Incredibles. He’s an annoyance whose only function seems to be to help lure the teenage audience to this rather heady, dark, R-rated venture.

Oh well, casting director Denise Chamain probably can’t win every battle.