While blessed with entertaining performances and uncommon earnestness (for a Hollywood movie) about the tribulations of middle-aged romance, there's something a little too artificial about "Something's Gotta Give."

Taking place largely in a Hamptons beach house (that is quite obviously a soundstage) where a divorcee playwright (Diane Keaton) has been duped into acting as nurse to an aging playboy (Jack Nicholson) after he's had a heart attack while fooling around with her flighty daughter (Amanda Peet), the film's snappy sense of humor is all too often undercut by affected romantic chemistry and by the overuse of facile cinematic conventions, like musical montages of characters laughing, talking and drinking wine while the camera circles them in the candlelight.

As written and directed by Nancy Meyers ("What Women Want," "The Parent Trap" remake), the unlikely love story that forms between Nicholson (who prefers "the complete, uncomplicated satisfaction of the younger woman") and Keaton (who has been adjusting to independence and getting over old-fashioned notions of spinsterhood) is a source of sophisticated laughs -- with the occasional low-brow guffaw thrown in for good measure (say, Nicholson's posterior peeking out of a hospital gown).

But the film is lucky to have such charming, illustrious stars, because while sparks don't exactly fly, Keaton and Nicholson bring similar senses of whimsy to the roles that almost make up for the over-polished nature of the script, in which every breath they take feels scrutinized, analyzed, tested and optimized for both light-hearted nimbleness and maximum meaning.

Keaton shines brightest as an accomplished but charmingly neurotic woman who tries to be cool and go with the flow when she arrives at her beach house to find her 29-year-old daughter fooling around with a man more than twice her age. She also gets the most interesting conflict to explore because in addition to having an unwanted houseguest stirring some dormant passions, she finds herself feeling a tad hypocritical when she's unexpectedly pursued by the 36-year-old heart doctor (an appealing but miscast Keanu Reeves) whose insistence that his patient stay put is what got her into this fix in the first place.

Nicholson is also at the top of his game, playing up his bachelor persona with a impishly arched eyebrow and getting many good laughs out of his character's impatience for a medical green light to resume his sex life and out of his incongruous discomfort with falling in love -- let alone falling for someone who is actually close to his own age.

Meyers and her characters approach this relationship with an intelligence and tenuous maturity in which both parties are trying to step out on a romantic limb while still remaining emotionally indifferent. But while the director infuses this relationship with a grown-up wit, she doesn't find much depth. Nicholson's emergence from his romantic Peter Pan syndrome is more obligatory than sincere and Keaton is stuck bringing life to a stock symbol of the conflict many single women of a certain age feel between traditionally ingrained desires and the hard-found joys of self-sufficiency and self-determination.

These choice actors (including Peet, in a splendidly blithe performance, and the sublime Frances McDormand as Keaton's flirty feminist sister) seek out the comedic nooks and crannies of their characters souls, but while "Something's Gotta Give" is reliably amusing, Nicholson and Keaton aren't done justice by the picture's plot, which incorporates many extraneous, elongated twists and turns of the heart on its way to the pat ending you always knew would come.