Crackdown tries to combine elements of sandbox games, light RPGs and platformers to deliver an experience that is strangely familiar, while being inventive enough to entertain for a few hours at a time. How much you get out of the game depends heavily on how you try to experience it.
The premise of Crackdown is that you are a genetically engineered clone developed to bring a city back from the edge of chaos. You get to select how your male character looks at the start of the game, though this does not influence the gameplay. As you wipe the city clean of three vicious street gangs, your powers increase, making you a fierce law enforcing machine.
If you think of it as a cousin of Grand Theft Auto - which would make sense, given that the developers of this game were involved in constructing the first three GTA games - you may find the game the dumb ugly cousin. It borrows from GTA clumsily. Allowing your "good-guy" hero to rudely rip people out of cars is a blatant rip-off of the gangster sandbox genre and it doesn't fit into the theme of the game. You are punished for killing too many civilians, but the game is structured to make running them over too easy and visually rewarding. Millions of gamers have grown used to this tongue-in-cheek human roadkill, but it doesn't fit elegantly into a game about superhero cops.

If you approach Crackdown as a driving game, you may find it more frustrating than fun. Driving suffers from two problems. First, the map is designed to be heavily vertical, with 75% of the action taking place above your head. Because of this, driving is essentially optional for most missions, with the map taking up a very small footprint, relative to previous sandbox games.
Second, the driving controls are intentionally awkward at the start of the game. In a catch-22, the game's driving doesn't get to be really pleasurable until after you've been able to build up your character's driving attribute. You can't get there if you don't drive an awful lot. But, you won't want to drive an awful lot until your abilities improve. Tough trick to pull.
Driving gets to be the most fun once you have maxed out your character and experience the morphing cars. The three agency vehicles - a sports car, an SUV and a tractor trailer truck cab - get tricked out and add abilities as your character does. The rides build features like machine guns - which replace the horn - or fat tires with a hydraulic jump that let you hop onto rooftops. Unfortunately, the full game keeps to only three agency cars and no other automobiles on the map will morph with you.
Jump into Crackdown as a lover of platformers and you will probably be pleasantly surprised, and maybe even hooked. Critics of the game's map size are missing the most important element of the game. At its heart, Crackdown is a jumping platformer, where you can spend hours navigating windowsills and roof lines to collect the 800 orbs scattered across the city. I love jumping through the city to obsessively hunt down the 300 hidden orbs, which increase all your skills at once, and the 500 agility orbs, which make jumping even more intoxicating as you gain agility.