May be considered a rival for Gran Turismo 4
In the world tour, you'll start your career as a race driver and evolve along the game, and you will have a technician explaining all the details of what's happening with you and your car, during the race. For example, he tells you if your engine or other part is broken, if you are driving amazingly, if you are near the disqualification. A precious help indeed.
The world tour races are splitted into tiers: there are near 35 tiers, each one containing more or less 3 races. As you complete one of the races of a tier, you unlock the next tier. The cars are are the default ones, you cannot choose another. Right before the race starts, you can save your progress or modify some characteristics of your car: transmission, tires softness or hardness, suspension, etc.
Once you achieve all the wins in all tiers, you're claimed the world race driver champion.
The pro career isn't much different. Instead of tiers, it has cathegories. Each cathegorie represents a different type of racing: classics, rally, offroad, gt, formula, etc.
It is a successful game.