Flat Out is simple and fun
As for the mini games, I have found that the small races and demolition derbies are the most fun. The target and distance games are pretty cool, but are to repetitive to have lasting value.
Multiplayer is pretty much limited to split screen at this point in the original XBox's life, but it it still quite fun. When racing a friend, you tend to ignore the race and spend time trying to destroy each other's cars.
I would recommend this to anyone that enjoyed burnout but want's more off-road racing and more obstacles.