Forza Motorsport is a sim racer for the Xbox 360. I haven't really dug deep into the racing game genre, having only played Need for Speed Most Wanted and Burnout Revenge up until this point, but I can definitely see that Forza 2 has some real quality. The racing engine is tight, but the most addicting aspect to this game is building up a collection of cars, and painting them.
Racing
This game is sim racing at it's very best, with only games like Gran Turismo rivalling it. The racing engine is highly

On the multiplayer side, the racing has been entirely lagfree for me, although I didn't really dig deep into the multiplayer. Looking at the other dudes' cars is nice though, since Forza 2 has an incredibly paint tool to personalise cars.
Car collection and painting
Forza 2 has a large amount of licensed cars from all over the world to unlock, tune and paint to your heart's content. I believe there are around threehundred cars in the game, and attempting to get them all can be really fun, and will take you hundreds of hours.
Forza 2 has one of the most in-depth painting tools I've ever seen. With enough skill, you can create pretty much anything, which has of course spawned a huge amount of porn cars. Attempting to sell these can get you banned

The game also has a large amount of tuning options, just about anything can be optimized in your rides. You can build insane vehicles with performances that go through the roof.
Forza motorsport 2 is a very good sim racer, but personally, I'm more of a fan of the adrenaline pumps you get from games like Burnout. If you like collecting cars though, this game will definitely give you your fill.