What Happens in Vegas is a mix of sour and sweet, as Kutcher and Diaz's combat eventually turns to affection; the film also benefits from a great supporting cast. Rob Corddry, Queen Latifah, Dennis Miller, and Zach Galifianakis, among others, provide solid laughs whenever the film slows down. Director Tom Vaughan keeps the pace brisk, and that swiftness keeps What Happens in Vegas from bogging down or becoming a chore. It tries to follow the template set by Judd Apatow's recent successful comedies like The 40-Year-Old Virgin and Knocked Up, mixing naughty, bawdy jokes with sweeter, more sincere sentiments; while the execution may not be as impressive here as it is in Apatow's films, it's also far better than anything the Farrelly brothers (The Heartbreak Kid, Me, Myself and Irene) have made in years. What Happens in Vegas isn't a comedy jackpot, but it's hardly a losing bet.
Even as their unwelcome marriage becomes a battleground over possession of the money, anyone who doubts that Diaz's busy go-getter and Kutcher's slacker will learn from each other, come to respect each other, and, in time, have real feelings for each other has clearly never seen a romantic comedy before. Neither Kutcher nor Diaz are working much outside of their established personas here -- he's an overgrown child, and she needs to loosen up -- and their on-screen chemistry is a bit more convincing when they're angry than when they're not, but they do get a nice rhythm going.