Isla Fisher, a steady scene-stealer in films such as 2005's "Wedding Crashers," 2007's "The Lookout," and 2008's "Definitely, Maybe," receives her first lead role in "Confessions of a Shopaholic." She is irresistible, lighting up the screen the same way Julia Roberts did in 1990's "Pretty Woman." The project, regrettably, is not playing on the same level. Based on the novel by Sophie Kinsella but seemingly more inspired by "Legally Blonde" and "The Devil Wears Prada," the movie strains to follow the tried-and-true formula of a perky fish out of water who is in over her head but with the determination and intelligence to prevail. There is nothing wrong with a little female-empowerment, but virtually everything about the film seems stolen or borrowed, and done better the first hundred times around.

25-year-old Rebecca Bloomwood (Isla Fisher) is a New York City journalist with one very expensive addiction: shopping. Having maxed out all twelve of her credit cards, Rebecca tries to claw her way out of debt by nabbing a job at hotshot fashion magazine Alette, but is turned away before she has even interviewed. Despite being the last person worthy of advising others on money issues, she finds herself with a much different writing job at financial publication Successful Saving. Much to her own surprise, Rebecca finds an honest angle to write from and has soon made a big splash with article "The Girl in the Green Scarf." As she continues to contend with work, debt collectors, and the inability to walk by a storefront window without going inside and purchasing something, she also starts to fall for editor-in-chief Luke Brandon (Hugh Dancy). He doesn't yet know about the secrets she kept from him in order to get the job, and it is only a matter of time before Rebecca's fraudulent facade is cracked open.

Director P.J. Hogan (2003's "Peter Pan") fetishizes name-brand clothing in "Confessions of a Shopaholic"—Rebecca more or less orgasms the first time we see her enter a store—but he doesn't pay half as much attention to setting his story in the real world. Sure, Rebecca is faced with serious money woes as a result of her spending, but she also never seems to be in any real trouble. Best friend and roommate Suze (Krysten Ritter) tells her to not worry about paying rent. Luke gives her a job because, well, he thinks she's adorable. Despite the viewer only getting to hear the first two sentences of the inaugural article she writes, her magazine column becomes the toast of the town overnight. Yeah, right. And let's not even expound beyond mention her claims of speaking Finnish and her coincidental run-in with some business colleagues hailing from Finland.

The film isn't without amusement—it is very funny, for example, when Rebecca mournfully says of a store where she is behind on her bills, "They said I was a valued customer, and now they give me hate mail"—but the script by Tracey Jackson, Tim Firth and Kayla Alpert never rises far above stereotypes and emotional pandering. A scene scored to Greg Laswell's gorgeous ballad cover of Cyndi Lauper's "Girls Just Wanna Have Fun" might have been a whole lot more touching were the relationships involved in this dramatic segment—one between herself and her frugal parents (John Goodman and Joan Cusack), and the other with Suze—developed beyond types. Rebecca, alas, is the only person in sight with a palpable history and depth, and her bland, predictable romance with Luke only gets in the way of what could have been a pert and fascinating character study. She is a strong, appealing young woman who doesn't need a man to define her, so why must her story end on such an archaic note?

Isla Fisher has such an inviting, funny, down-to-earth presence that she almost single-handedly makes "Confessions of a Shopaholic" worth recommending. Almost. As Rebecca Bloomwood, she is shameless in doing whatever it takes to get a laugh, but she also has a soulful quality that allows the viewer to feel for her. There are a couple moments in the picture where the camera lingers on Fisher's face, and the levels of complexity she is able to rustle up without saying a word is pretty astounding. The rest of the ensemble is squandered, or miscast. Hugh Dancy (2007's "Evening") is far from her match as love interest Luke Brandon, who doesn't share enough chemistry with Fisher to make an impression. Krysten Ritter (2008's "What Happens in Vegas") is an odd choice as Rebecca's best friend Suze, exhibiting a detached iciness that doesn't work for the character. As Rebecca's parents, John Goodman is playing a less dimensional version of Pops from 2008's "Speed Racer," while the great Joan Cusack (2008's "Kit Kittredge: An American Girl") only gets one funny moment, attempting to cut the tiniest sliver of cake for glitzy, wafer-thin fashion magazine owner Alette (Kristin Scott Thomas).

"Confessions of a Shopaholic" has one marginally original element: the use of mannequins as live embodiments who speak to Rebecca. Though they are there as a device to tempt her to buy expensive frocks, they are unnervingly creepy, one pick-axe away from chopping our lovable heroine up into itty-bitty pieces. This oddball step into flights of horrific fancy notwithstanding, the film is a lightweight, cotton candy confection with too much sugar and not enough tartness in its satiric aims. It's been-there, done-that to the nth degree, and not even a radiant star performance is enough to chip away the mold from a derivative plot that can't be believed for a second.