"Chaos Theory" shows just how crucial casting can be to a movie, especially something as sensitive to nuance, idiosyncrasy and timing as a romantic comedy.

Ryan Reynolds, an actor with good looks and a rich seam of intensity, was amusingly arrogant as the six-pack-abbed vampire slayer in 2004's "Blade: Trinity." But in "Chaos Theory," an edgy romantic comedy about the giddy ecstasies and gloomy doubts of being in love, he's about as hilarious as a funeral director at a wedding.

He plays Frank Allen, a control freak whose sure, steady life is rocked by a series of darkly comedic misunderstandings, which causes his wife (an appealing Emily Mortimer) to believe he's having an affair. But he's pitched way too sharp and edgy to be endearing. We couldn't help wondering what a comically assured performer, such as Jim Carrey, would have done with the role. After all, Carrey had a similarly life-upending role as the lawyer suddenly forced to tell only the truth in "Liar Liar." In that 1997 movie, we looked forward to every possible permutation of the premise, thanks to Carrey's ability to surprise.

But in "Chaos Theory," Reynolds's performance is taut, crabby and tense. And his beard and glasses, which intensify those already narrow eyes, suggest a mad bomb-builder rather than a hapless soul with whom we can identify. Instead of making us laugh with a grimace at his long string of bad luck, he just makes us grimace at him.

-- Desson Thomson (April 11, 2008)

Contains profanity and sexual situations.