While the single player is a solid game in itself, the multiplayer is where the game really shines. You can upgrade your cars with money you win from races. That's also how you get new cars, you buy them with money you've won from races. You don't have to finish in the top 3 to earn money, everyone earns money in a race. The higher you finish the more money you make though. Most of the cars are level locked in Multiplayer. There are 30 levels for your driver to work towards getting. There are also a ton of visual customizations you can apply to your cars. There are 50 cars in the multiplayer to race with.
Each car handles like it's real life counterpart. To some this will seem too difficult and they will give up quickly. But, if you stick with it for a few hours you will quickly get the hang of it. How you drive is completely up to you, you can power slide around most corners or slow down and accelerate out of a turn like a real race car driver would.
There are so many track I couldn't tell you honestly how many there are. lol It will take you a little while to learn them all. Some of the tracks are real racing tracks and others are made up city tracks. All are interesting, detailed, and challenging. There are several different types of race events as well: time attack, checkpoint, live routes, drifting, racing, etc...
This is a must have game if you're into online racing games.