First things first: Midtown Madness 3 belongs in your collection, and not because it's the greatest racing game ever. In fact, it's far from that. If you want the greatest racer of all time, get Gran Turismo 3. Where MM3 shines is its fun factor. Sitting down with some friends or playing over Xbox Live, this game is a blast.
Don't take my word for it either. If you haven't already subscribed to Xbox Live, you need to. Otherwise, you'll probably just get bored with MM3 and toss it aside. The online capability is the reason to buy the game, as it is the reason the game was developed in the way that it's presented to you.
Essentially, MM3 is your typical checkpoint racer that pits you against the clock to complete a set of tasks or reach certain places within the cities of Paris or Washington, D.C. within a given amount of time, similar to Crazy Taxi, Midnight Club, etc. Go online and the maps expand, making the game even more challenging.
Since you'll be playing against live opponents, there are no worries about crappy A.I. Thankfully, MM3 was designed with physics more as a guideline than a set of strict rules. Cars whip around corners with no problem and hitting other cars sends them flying like meaningless debris. This increases the fun factor in that you're not going to be handicapped excessively by random traffic that gets in your way. However, too much and you will be slowed down.
With physics as an afterthought, the game just bleeds arcade racer. Rarely do I have so much fun playing arcade racers. Additionally, the online capability just makes the game hemorrhage fun. Obvious though it may be, this game assuredly belongs in every red-blooded Xbox-owning (Live-subscribing optional) person's collection.