Juiced's Economy system is a simple test of reality.The need to improve your cars is what NFS lacks.
As you move on with the career, you can see that changing back to the car you first used (in early game) you can still win the races. I felt very disappointed when I did this (Try it!). It takes out the reason for improving the cars!
In Juiced this is entirely different, because every car has its own properties and power. To control that you not always face incredible powerful cars there is a system of categories implemented. The races have a minimum and a maximum power for the cars to be able to enter the event. So, in this way, if you enter a race which has a top power of 400 HP with a car of 200 HP is very likely that you face cars that have more speed and acceleration that your own. This is why you must tune your car for th events.
Another excellent aspect of this game is the Economy system. As the official review of Game-spot says, you can have a very wide stock of cars in one point, and loose them because you lost too many races that have entry fees or lost too many bets. But this is not a negative issue! It's excellent because you should not enrol in a race to loose it! The point is to win, right?
The Economy model also takes into account car damage. After every race, you must repair the car according the damage you've inflicted to it. This helps you to race better, because you avoid hitting the walls and other cars at full speed. Again, it is not a negative issue, unless you can't drive well.
All these aspects make Juiced a game in which YOU CAN LOOSE, unlike many modern games. It might be frustrating to have 15 cars and start selling them in order to win some races, but that gives an extra push towards making an effort.
Do not mistake my words. I like NFS. In fact, I am playing Most Wanted Right now, but it has some flaws that won't be corrected because is a game intended for those people who like seeing speed and smashing things with a 150,000 U$D car, not for people who enjoy Racing.
The graphics in Juiced are not as good as in NFS series and the speed is not as well modeled as in that series, but they are still good graphics.