Forza Motorsport 2 truly must be one of the few sequels in motor racing game history that doesn't try shatter boundaries and start amazing new things. It simply takes the original Forza (by itself a fantastic racing game) and polishes it to a gleaming mirror. All the little bits that are good in Forza, are excellent in Forza 2. The modification system is improved, the car selection better, the visuals stunning. And just to cement it more, progress is rewarded at every step.
Of course, no man can really review a modern racer without comparing to the big daddy of modern realistic racers, Gran Turismo. Having hired a PS3 and GT5 Prologue for a geeze at the new title, I went back to the old faithful Forza 2 feeling even better about it. Although it lacks some of the fanciness (in-car views would be a bonus), it DOES compensate with a significantly more refined physics model.
The online multiplayer is pretty good too, the only disappointment is (like most Live titles) the lag involved. Sadly the lag compensation system is a catch up type setup which can result in opponents cars being catapulted either past you or through you in some circumstances. The community are generally good too.
In summary, if you're looking for a racing title that just looks pretty and forgives sloppy driving, there's other titles that meet that criteria. But if you want a no holds barred, serious racing game with huge depth and realism, look no further.