Colin McRae: DiRT 2 for Mac is an excellent rally racing game which recreates all the excitement of rallying.
Colin McRae: DiRT 2 sees you take on the best circuits in the world in competition racing or time challenges. The graphics are excellent and collisions in particular are very realistic. It's definitely a step-up from Race Driver: GRID.
The gameplay is also excellent, although it's not easy to master at first. The soundtrack and music complement the game perfectly alongside your co-pilot who tries to guide you with hints and tip about how to take corners and precarious parts of the course.
The main HQ in Colin McRae: DiRT 2 is a motor home where you have access to all of the games features. The game includes many events, the ability to purchase new cars with the competition money you earn and compete on dirt circuits etc. There's also a an online multiplayer mode.
A steering wheel would help you get a lot more out of the game and the keyboard controls aren't great in Colin McRae: DiRT 2 but overall, it's an excellent racing game for Macs.