While the gameplay might not be as good as the classic Rallisport Challenge 2, it looks amazing and the online is great.
I didn't give the game a 9 for two main reasons. The first reason is that while not terrible, the gameplay could have been a lot better, taking this from a fun and stunning looking game into the realm of racer nirvana. Rallisport Challenge 2 is what most gamers refer to as simply spot on perfect arcade style offroad racing. Fun and accessable, but you still feel the weight of the cars.
Dirt 2 still feels too light and the over/under steer problems can be a very annoying aspect of the gameplay if you don't learn how to figure the system out. Its annoying that you have to adjust to the light physics so much,but if you can manage to get used to it, you will have a lot of fun playing this game. The online aspect of the game is where it really shines. I never have any lag problems and racing through these types of dirt tracks with offroad style vehicles is just flat out fun.
The graphics are some of the best this gen so far. The lighting is amazing and the environments usually look fantastic. The voice chatter while you drive is lame but you can turn it off if you find it as stupid as I did.
The single player seems pretty deep so far and the online is what I really love so far. My other gripe that kept the game from AAA status is that it is moving too far away from a rally game. There are not nearly enough point to point rally races in the game. I don't like how much time you have to spend racing trucks and buggies. They are still fun, but the heart of this game should be rally cars and true rally style races. It's not the end of the world by any means, it just keeps the game from being as amazing as it could have been. In my opinion at least.
Bottom line: If you like racing games, especially offroad racers, and you can forgive arcade style gameplay, then you will have a very large amount of fun playing dirt 2, especially the fantastic online part of the game.