I'm not a big racing game fan, but I didn't hate the game. It gets monotonous but with the ability to hire a driver you can get past it. If you like racing games and time consuming achievements, pick it up. Otherwise, stay away from it.
The majority of the single player is easy since you can hire a driver. There is some stuff you have to do yourself like the time trials, but they are doable. The "hard" part if finding enough people to boost your 1,000,000 credits. It takes around 5 hours of actual racing on your part but the boosting session can take all day if you are boosting other people at the same time.
Question to the boosters of Forza 2; Is it worth purchasing, I have the third, I absolutely love it, and the achievements are not difficult at all, no boosting requried. Is this game difficult to max out also?