This is a great game and for 19.99 is a great buy, next cheapest I have seen it is play.com for 24.99.
Here is a description of the game
Brilliant experience from a legendary game designer. From Dave Jones, the creative mastermind behind Grand Theft Auto and Lemmings, comes Crackdown, an explosive masterpiece set to define open-world, free-form next-generation gaming.
True next-generation visuals. Harnessing the power of Xbox 360, Crackdown players enforce justice against the backdrop of a crime-ridden metropolis that is massive in scale, monstrous in scope and meticulous in detail.
Cooperative gameplay for double the mayhem.
3-D free-form gameplay. For the first time ever, an urban playground has been created to encourage players to explore and exploit the full width, depth and height of a city. Players wage war on the crime syndicates by taking part in high-octane chases on foot and on wheels while using any appropriate route along, around, across, over, under or through the environment.
Over-the-top action. All strategies and tactics are acceptable, provided players reclaim the streets by unleashing the awesome abilities inside each agent. As players develop and hone their gameplay skills, their agent's genetic tendencies will increase, allowing players to realize their agent's full potential. Players will be able to run at dazzling speeds, take death-defying leaps, handle the most incredible weapons, perform impossible vehicular maneuvers, move massive objects and deliver bone-crushing blows.
Music as environment. More than 100 licensed tracks, spanning a wide range of styles and genres, give audio identities to characters and locations
The environment as a weapon. Is a character low on ammo? No problem. Thanks to an amazing amount of props and a deep physics system, players can use whatever they can get their hands on as weapons - trash cans, vehicles, even people - to clean the streets of crime.