96 minutes

In theaters May 9, 2008

Rating: PG-13, Romantic comedy

Jack and Joy are girl and boy whose love is nevermore. But judge decrees, "Stay married, please," so now begins the war.

Maybe I should just stay with prose, and maybe this flick should have just stayed away from Vegas.

Because the first act, set in Sin City, is loud, frantic, strained, ham-fisted, and off-putting, with little of note other than the enthusiastic and obnoxious product placement.

Then What Happens in Vegas moves to New York, and things pick up considerably.

WHIV is a battle-of-the-sexes comedy that revolves around two New Yorkers, played by Cameron Diaz and Ashton Kutcher, who've just met. Joy and Jack -- she's a commodities trader (which neither she nor the script makes in any way convincing) who just got dumped, he's an underachieving party boy who just got fired by his own father -- wake up together after a very wild and very drunken night in the Neon Nirvana.

Not only are they hung over, they discover, but they're married as well. And they immediately recognize their everlasting hate. So they both want out and they both want away and they both want both quick.

But Jack uses Joy's quarter on a slot machine and, wouldn't you know, wins, yep, three-million bucks.

Jack wants that money. So does Joy. But they want a quick, easy divorce as well.

They return to New York and request an annulment, but the judge, played by Dennis Miller, refuses their request, freezes the money, and instead sentences them to six months of hard marriage, decreeing that they must set up housekeeping and try for half-a-year to make their union work.

Thus begins an Odd Couple-like co-habitation (she's a neat freak, he's an uncouth slob) crossed with a War of the Roses-like matrimonial skirmish, during which each of them seeks and gets help, advice, or criticism from a close friend (Rob Corddry, Lake Bell), a boss, (Dennis Farina), a parent (Treat Williams), or a marriage counselor (Queen Latifah) while attempting to trick the other party into demonstrating unfitness as a spouse and thus relinquishing all claims on the seven-figure moolah.

The director, Tom Vaughan (Starter for 10), works from a screenplay by Dana Fox, who wrote 2005's similarly uninspired and unpersuasive The Wedding Date, which starred Debra Messing and Dermot Mulroney.

The predictability of the narrative is to be expected -- as is the case of the vast majority of romantic comedies -- and isn't really all that problematic. But there's a staleness and an unevenness that undercuts those few moments where truly funny interplay or legitimate emotion registers as worthwhile and watchable. The sheer joy and release of expressing dissatisfaction and vitriol bring the second act to life, but the spell it casts doesn't last.

Kutcher is a natural and skilled comedic actor, and Diaz knows how to hold the screen with her smile if nothing else, but we weary of watching them once the good-scene-bad-scene-good-scene-bad-scene pattern is established.

The comic highlights come courtesy of the supporting turns of Rob Corddry and Lake Bell, both of whom are consistently amusing as the respective best buds in this up-and-down comedy about marauding marital misery.

The main characters in What Happens in Vegas hit the jackpot. Those of us watching over their shoulders as they slide the coin in the slot, however, do not.