Granted this is one of those lame mini-game based girl games (like Oshare Princess or... the one Konami made last year), but for what it is they added a lot of stuff.
-You do street races (3-4 mini games depending on the area) to gain points. You spend those points to get parts for your car.
-Each part has a value that helps in drag races and another value that helps in the custom contest show.
-Drag races (another roulette-type minigame, one spin for each gearshift) help you gain supporters, which help you for ONE custom contest show, and then they reset.
-After 6 days of street races or drag races (you choose each day) and setting up your car, there is a custom car show. The show is like the drag races, except you score is multiplied by the number of supporters and parts are judged by their looks rather than their function.
In addition you pick the type of car you want, little cars have less horsepower, but parts are cheaper. Other types are more popular, but might be slow and more expensive. There's a lot more to the game, but you have to beat the first chapter which is a pain. The biggest problem with the game is a lot of it can be chalked up to luck which in turn requires a lot of save/resetting. That and there isn't really much of a 'game'.