When Lerner and Loewe wrote and composed the song "Thank Heaven for Little Girls" for the 1958 musical "Gigi," it's a safe bet they weren't referring to someone like the pint-sized, foul-mouthed, guns-blazing 11-year-old Hit-Girl (Chloë Grace Moretz) in "Kick-Ass." And yet, the message of the title still applies. A superhero movie with blood, guts, salty language and an acerbic sense of humor, the film flies in the face of a genre that, with the exception of 2009's "Watchmen," usually tames things to a PG-13 level and targets the under-17 crowd. "Kick-Ass," however, revels in its rebelliousness, writer-director Matthew Vaughn (2007's "Stardust") and co-writer Jane Goldman wisely choosing to adapt the comic book by Mark Millar and John Romita Jr. outside a Hollywood studio system that urged them to water down the material. Vaughn's leap of faith that he would be able to sell it after the fact paid off, with buzz building after initial screenings and Lionsgate swooping in to purchase distribution rights. Is "Kick-Ass" everything it's cracked up to be? Well, no. Strip it of its rude behavior and more graphic violence and it's basically just a lower-budgeted retelling of "Spider-Man." The picture's saving grace, then, is Hit-Girl, an exuberant cinematic original destined to become iconic. Without her, as the saying goes, the makers would have nothing.

Tired of being a teenage nobody, comic-loving Dave Lizewski (Aaron Johnson) wonders to his friends Marty (Clark Duke) and Todd (Evan Peters) why there aren't real superheroes in the world. Secretly, he has bought a green spandex outfit and matching mask and begun wandering New York City fantasizing about jumping from buildings and saving people in need of help. His first attempt at the latter goes disastrously—he ends up stabbed in the stomach and subsequently hit by a car—but once recovered he tries again and becomes a YouTube sensation. The media quickly catches wind of this costumed mystery man known only as Kick-Ass, and so, too, do actual vigilante superheroes Big Daddy (Nicolas Cage) and Hit-Girl, a deadly father-daughter team who believe he has potential. Every story of this kind needs a villain, and here it is super-wealthy, ultra-dirty mob boss Frank D'Amico (Mark Strong). Frank wants Kick-Ass' head on a plate and is willing to use his own teenage son Chris (Christopher Mintz-Plasse), under the alter-ego Red Mist, to smoke him out. What Frank doesn't realize is that it is actually Big Daddy, a former policeman he framed and sent to prison years ago, whom he should be worried about.

"Kick-Ass" is overlong and kind of unwieldy—at 117 minutes, it could have been tightened and strengthened with a good fifteen minutes trimmed out of the middle—but there is never any doubt about director Matthew Vaughn's passion for the project. Comic book and superhero lore are liberally referenced as the story looks to find out what it would be like if regular people in the real world tried to be crime-fighters of the Batman or Spider-Man sort. Clearly, Dave is mortal and has no superpowers, but in today's day and age of technologically advanced communication it makes no difference; all it takes is for onlookers to record Kick-Ass fighting a group of thugs and post it to the Internet and he is an immediate celebrity with a fanbase and even an upcoming comic book based on him. Meanwhile, Dave must keep Kick-Ass' identity secret while also putting on a façade for the girl he likes, Katie (Lyndsy Fonseca), who assumes he's gay and relishes the fact while holding tanning sessions and sleepovers with him.

Aaron Johnson (2006's "The Illusionist") is a capable lead as Dave Lizewski/Kick-Ass, but the character is difficult to identify with since he lives part-time in a fantasy land and clearly has some psychological problems and a death wish. With a mother who died a year before of a sudden aneurysm, Dave is also frustratingly distant from his widowed father (Garrett M. Brown), who makes an effort to be close to his son without any of those feelings reciprocated. The actors surrounding Johnson in supporting roles are more fun and make bigger impressions. Christopher Mintz-Plasse (2007's "Superbad") breaks out of the McLovin mold to coolly play Chris D'Amico/Red Mist, spoiled son and inevitable successor to father Frank's business. Mintz-Plasse isn't yet a bad guy—when he discovers Kick-Ass is innocent, he tries to warn his pops and save his unlikely new friend—but all signs point to him being easily swayed to the dark side if it means gaining all the power. Nicolas Cage (2009's "Knowing") is tortured yet subversively kind as Damon Macready/Big Daddy, his offbeat but loving relationship with daughter Mindy/Hit-Girl as close to an emotional anchor as the film has. A moment's thought to how he has brainwashed his child and turned her into a remorseless killing machine sort of puts a damper on the warm and fuzzies, but their bond remains strangely sweet.

And then there's cute little pig-tailed Mindy, going bowling and making hot chocolate with marshmallows when she's not swinging knives around, wielding swords, and blowing brains out as purple-wigged Hit-Girl. Amazingly confident and assured, Chloë Grace Moretz (2010's "Diary of a Wimpy Kid") gives a breakthrough performance bound to be talked and raved about for years to come. Admittedly, there is a tinge of discomfort in witnessing a little girl murder so many people without batting an eyelash, but they are bad guys she's dispatching of and she's never less than adorable even as she's uttering any number of choice four-letter words. When Moretz is onscreen, the film's weaknesses—most of all, its routine plotting and occasionally meandering pacing—wash away. She's that bold and entertaining of a presence.

"Kick-Ass" doesn't have a $100-million budget, but director Matthew Vaughn uses his funds judiciously and saves the best set-piece, set on the top floor of Frank D'Amico's Manhattan skyscraper, for last. Overly flippant in its depiction of lives lost but not meant to be taken any more seriously than a silly comic book, the film is high-spirited and blessedly un-PC in the way it makes no excuses for what it is and never conforms to what other people might be expecting. With that said, conventions remain intact, and that includes a delicious setup for a sequel that one imagines might actually be superior if this first film becomes a critical and audience sensation. Just one request: make Hit-Girl the rightful lead she belongs to be. She's already a star.