Forza 3 multiplayer can be summed up quite simply: you make the rules so go do whatever the hell you want.
There are about 60 rules you can set for a multiplayer match that allow you to create just about any game type you could want. Instead of having a gentleman's agreement at the start of the race to play Cat & Mouse, you can now make someone the mouse. You want capture the flag? You can make it happen. With so many options, the only limit is your own ingenuity. You can force teams of any size (all against one, three-on-three, whatever you want), give one person the "heavy" car and the others faster vehicles. You can force specific camera modes if you want everyone to play from the dashboard view and even require the use of manual transmission with the clutch (Left Bumper).
No more guessing at scores of games you had to make up in your head. Now you can create rules that are tracked by the game with relevant points. These sets can be saved, of course. For those who hate setting all these options, Turn 10 will create its own set of game modes for parties to hop into. Thanks to the magic of Xbox Live, Turn 10 can keep track of which options are used most, what game types are the favorite and then adjust the official hoppers to suit the community.
Now if only we could convince them to set a match type of King of the Hill with all Penis-Mobiles.