Two of the most respected, famous, talented individuals in movie history - Jack Nicholson and the late Peter Sellers - have and had off-screen relationships, both professional and personal, at complete odds with their on-screen personas. In terms of his primary professional career - as a comedian - Denis Leary has a persona which can be described as harsh, earthy, laced with profanity, and with characteristics which often are vulgar. He's also very funny, but even those of us not averse to comedy with very adult language and demeanor can find some of his stuff off-putting on occasion. But on-screen, while he also presents some rough edges, in this film (as in "The Ref") he is likable, and is a also a competent actor (if not yet a "Sellers" or "Nicholson") who provides an engaging performance. In "The Ref," the splendid supporting performances by Kevin Spacey and Judy Davis, his neurotic hostages and later allies - along with the rest of the excellent cast - added to the film's enjoyment. In "Double Whammy" the beautiful and talented Elizabeth Hurley (Hugh Grant should have his head examined) and the other, supporting cast members, many recognizable for other capable performances, add to this film's enjoyment, as well.
But, back to comparison with Sellers and Nicholson, Leary is a man who in real life had been married to the same woman for nearly 25 years, half his entire life, who has significant charitable activity, who taught English (IN COLLEGE), and is as stable as these two were not - in reality.
We certainly can enjoy performances which don't reflect actors' personal/real lives (if this weren't so, movies and other entertainment media might die-out) - but it's interesting to recognize the virtues of someone like Leary, especially since, ironically, I've encountered people who eschew his movies because the don't care for his on-stage comedy persona. In this film, albeit's not being "The Maltese Falcon" or "Basic Instinct," and Leary not yet another Bogart or Michael Douglas, it still is well-cast, well-acted, and provides a competent mix of humor, action, romance, some surprises/plot twists, and drama, to provide an enjoyable hour-and-a-half spent, and rates a solid 8* (possibly even higher).