Aside from several implausible plot points and incidents, there are moments in the movie when the main characters come across as entirely unsympathetic. The movie makers perhaps assume that the audience will overlook those moments because we're so enraptured by the characters and their madcap adventures and repartee that we forget what happened three seconds ago. (I'm surely giving the movie makers way too much credit here - I don't think they realize their characters are unsympathetic.)
[Minor spoilers ahead]
For example, Butler's character Milo punches a cop to the ground because he wants to get arrested and spend the night in jail. We're supposed to overlook this violent crime because Milo's motivation stems from his romantic feelings for Aniston's character Nicole.
In another incident, the villain's car overturns following a car chase and shoot-out. Before Milo and Nicole can catch him, he carjacks another car and escapes. The carjacked woman is abandoned on the side of the road - do our heroes call 911 or even ask if she's okay? No, the camera follows them bantering with each other as they search the car wreck for clues, and the woman is forgotten.
A third incident involves a colleague of Nicole's who has the hots for her. He follows her adventures at a distance throughout the movie and becomes unwittingly involved. He's kidnapped, tied up, has his leg broken with a golf club, and is injected with horse tranquilizer before being abandoned in a bad part of town (having said that, every part of town - Atlantic City - in this movie looks bad). He calls Nicole on his cell phone and tells her what happened. Tired of his romantic pursuit, she hangs up on him with a shrug. We're supposed to overlook this heartless behavior because... well, I don't know why. Because Jennifer Aniston is perky and likable?
Can you do this sort of thing in a novel? I can't imagine how these scenes could be written without the characters coming across as complete jerks. I can't imagine my critique group, let alone an editor, allowing characters to behave this way when the reader is supposed to be rooting for them.