Best racing game I've ever seen!
Forza has great graphics and audio. The painting system for the cars works well and gives the player a lot of power to customize the look of most cars. The car selection is great regardless of what type of cars you like. The racing classes are broken up well in order to place you against similar cars. The tracks give a lot of variety to driving conditions.
There are only a few areas where I think the game could improve. Naturally adding more cars is always a good thing (but Forza has plenty... 230+ to choose from). More flexibility in upgrading and customizing the cars would also be nice. I was a bit disappointed in how few option you get in upgrading the cars, but it does keep the game simple enough for anyone to play. Since there is also the ability to tune cars once they are upgraded, I can't really complain about this too much, but I would like to have more options for switching out engines in old cars for much newer engines.
In all, this is the best racing game I've ever seen. I would highly recommend it to anyone. It can be very addicting.