This game is so much fun, it's almost ridiculous.
The career is very linear, no open-world roaming, and has 9 Tiers that players progress through. Each tier has 6 events (races, checkpoints, destruction) and a one-on-one with a Rival. Each Rival has certain demands that the player must accomplish through the 6 events, such as Barging so many cars, or clean triple-nitro-ing, etc. It gives a nice sense of accomplishment when you complete a Rival's demands and are able to race them.
Playing the single-player campaign is fun, but the real fun is playing online or split-screen with other players. There are lots of game modes, from racing to motor mash (demolition derby) to team racing and more.
I have had an immense amount of fun every race I participated in, and like I said, this game is so fun, it's almost ridiculous. If you enjoy racing games, you have to play this game at least once; it's well worth it.