Vaughn's direction is nothing less than clever and kinetic. By employing video game techniques inspired by Shoot 'Em Up and Crank movies, Vaughn really excels at showing highly-stylized bloody violence on screen. As for the script, the main concept of an ordinary teenager who chooses to become a superhero is downright effective evoking loads of laughs and our sympathy. Aaron Johnson's cool, unrestrained performance also helps a great deal.
The film revitalizes the genre by undermining its rules. The characters involved have no special powers, most of them, no necessary backstory and no turning point that resulted in them becoming superheroes, much like in Watchmen. Despite this, the movie establishes its own pantheon of heroes and the director knows that there's nothing more fascinating than the battle between good and evil shown in a vivid, exciting fashion.
What's controversial about the film is the extensive use of pitch-black humor including the character of 11-year-old Mindy McReady aka Hit-Girl who has been trained from the early years to become a killing machine by her loving father aka Big Daddy. The whole subplot may be immoral for some who don't understand this kind of cinema, yet it's surprisingly plausible due to a tongue-in-cheek writing and acting talents of Chloe Moretz and Nicolas Cage who are as subversive in their respective parts as you can get. Last but not least, the artist formerly known as McLovin' channels a wannabe villain named Red Mist. You may be actually surprised by how smart he is in his plotting.
Overall, Kick-Ass is a refreshingly funny and wickedly entertaining spectacle that warrants the whole franchise of masked teenagers to come. 9/10 (A-)