Hollywood genre tip No. 43: In movies about heaven and hell, first make the audience care about the soul in limbo.

Seems pretty obvious, right?

The power of other films in the genre, such as “The Exorcist” and “Rosemary’s Baby,” emerged from their sense that evil might overcome good at any moment.

But in “Constantine,” this fight for the soul is a moot point, creating an unexpected and perplexing emotional vortex that tears apart the reality of many of the film’s characters and scenes.

As in the “Hellblazer” comic book series, John Constantine (Keanu Reeves) is a hero caught between heaven and hell. His soul has already been promised to the devil, and he is rapidly dying because of – what else? – smoking. Yet, he has the power to see the

supernatural spirits that fight a daily battle for the souls of mankind and destroys demons in an attempt to effectively buy his way into heaven.

Granted, it’s a tantalizing premise and a delicious twist on the standard good versus evil formula. It’s interesting that the person doing God’s work doesn’t particularly like heaven, is operating solely out of greed and, in one moment, gives heaven the middle finger.

The key here, though, is that the soul’s already been bought and sold, and the scenes that focus on Constantine’s morality and his inner struggles really have no weight behind them. With the end of the story already known, the suspense just isn’t there.

What is occasionally appealing, and what first-time director Francis Lawrence should have developed further, is Constantine’s existence in this in-between world.

He does travel to hell once, and it is a compelling – albeit brief – journey.

His descriptions to Angela Dodson (Rachel Weisz), whose sister has recently taken her own life, of the otherworld

and the special place in hell for suicides is the most entertaining subplot of the film, detailing the intricate chess game between the good guy upstairs and the schemer below.

Why Lawrence didn’t play up Angela’s later journey into the supernatural more will remain the film’s biggest mystery.

If the film had gone more in this direction, as a transparent, pulp episode of this epic feud, it would have been engaging and inviting in a way the morose and all-too-serious “Constantine” never is.

As is, every time the story pauses for yet another battle between Constantine and the CG demons, it’s an uninteresting digression that is more preoccupied with execution than substance.

Everyone’s so serious here. Reeves sneers, Weisz gawks, and only the devil (Peter Stormare) seems to have any semblance of a sense of humor. Usually, that’s OK in films like this. Here, however, because everyone already knows the ending, it seems odd they’d be so surprised, fearful or interested.

Hell, they’re taking it more seriously than the audience.