This game is definitely worth buying, not renting.
There are plenty of cars to drive, although some may be hard to get to unlock. Is that a good thing? Some yes, some no. If you just want to have a race with one of the nicer cars, then no. If you want a challenge and work for it, of course. The world racing and hot pursuit champoinships are extremely fun. I must admit, I am stuck on winning the last race on winning the last challenge, but I'm always up for a challenge. Do you want to beat a game in just a few hours? Of course not.
That is not the only thing good about this game. The cops chasing you is very thrilling, and the helicopters and spike strips make it all the better. Another thing is that you get to be the cops, with five different cop cars!
And last but not least, there's always the good multiplayer action. Grab a friend, and have a blast! Be the cop and have him be the speeder or vice versa.
This game is definitely worth checking out.