Carbon is the sequel to Most Wanted, but leaves alot to be desired.
Carbon starts you off driving down a Canyon towards Palmont in the heavily tuned M3 GTR you just won from a "badman" named Razor in MW. Here, a flashback of what appears to be a race between the 3 of the main rivals comes to the players mind. At the end, it shows you [Player] driving away. then Cross, former cop from MW turned bounty hunter, catches up. He trashes your car, you get helped by a gay looking dude named Darius, and start out buying a rubbish, 100 BHP car. You investigate what happened that night when you did a runner because you were a chicken, take down the three remaining rivals, get betrayed by Darius, wipe the floor with him, and thats it...
Carbon features the same gameplay as MW, with new events such as drifting and Canyon races injected. Cops are downplayed alot, with there being no need to be chased by them unlike MW.
The graphics of the game are just a more advanced version of that of MW. Nothing special.
I honestly had more fun glitching this game than actually doing the main career, such as accessing the Canyon (Link: http://www.youtube.com/watch?v=cYPIP3TrJME all content is MINE. I made this video) and free roaming in bonus cars (Link: http://www.youtube.com/watch?v=mhMjPHLPHBI Again, all content is MINE). So, be a good person and buy MW instead.