Aaron Eckhart stars as Adam in “I, Frankenstein.” (Lakeshore Entertainment/Lionsgate)

There’s an off-putting air of pomposity about “I, Frankenstein.” (Just listen to how self-important that title sounds when you say it out loud.) In fact, the aura of goofy grandeur is enough to scare some viewers off of the movie, an adaptation of Kevin Grevioux’s graphic novel about Mary Shelley’s monster, set in a modern-day dystopia being fought over by demons and angel-like gargoyles.

Don’t be frightened. The contents of the film are a lot more fun than the package looks.

Aaron Eckhart — his newly buff, fat-free bod covered with more stitches than a crazy quilt, and his handsome, scowling face a convincing mask of undead malaise — makes for a surprisingly deep and compelling antihero in this update of an antique monster movie for the Imax 3-D age. Frankenstein’s creature, called Adam for much of the movie before adopting the name of his scientist “father,” Dr. Frankenstein, is the consummate outsider: not quite human, yet unwilling to fully ally himself with either of the film’s supernatural warring parties.

He’s a zombie horde of one, in search of his own lost soul (and maybe a girlfriend), stuck between cosmic opposites.

On one side are the demons, ruled by the evil Prince Naberius (Bill Nighy, in fine fettle), who seek the secret to Adam’s reanimation, along with world domination. Yvonne Strahovski plays the pretty scientist who is trying to unlock these mysteries. On the other side are the gargoyles, an order descended from archangels and ruled by Queen Leonore (Miranda Otto). They only exist to protect us from the demons. More angel than demon, Adam is a kind of Avenger with a S.H.I.E.L.D., swinging a pair of sanctified cudgels that dispatch demons to Hell with a single blow. Yet he’s reluctant to join forces with the gargoyles.

The script’s religious themes are, at times, a bit much. Written and directed by Stuart Beattie (part of the “Pirates of the Caribbean” screenwriting stable), the film depicts a world where the forces of good and evil are uncomfortably literal. Yet, so what? It’s a cartoon, not a theological tract. And if Nighy’s Naberius looks like he’s wearing a Halloween mask whenever he converts from human form to demon, it’s really no worse than the squid head the actor wore in the “Pirates” films.

For the most part, “I Frankenstein” never takes itself too seriously. It’s also just respectful enough of Shelley’s source material to please more open-minded fans of the 1818 book. If it touches on notions of scientific arrogance and the question of what makes us human, it ultimately does so lightly, and with a mix of eye-popping action and loopy good humor. Like Frankenstein’s monster, this film grunts softly and carries a big stick.

★ ★

PG-13. At area theaters. Contains brief obscenity and violent action. 92 minutes.