Didn't unseat Mario Kart but I got a lot of kicks with this one.
Maybe I am biased because I am not much of a gearhead and I was successful at this game, but prior reviews that say the game is not fast clearly didn't even give it a chance. It only took me about a week or two of casual play to unlock all the tracks and racers and beat it on the highest difficulty, but the speed that is required to succeed on those levels is truly insane, you are going so fast that you have to have the tracks almost memorized to make it through without crashing.
It's not even in the same league as Mario Kart but for the casual driving fan who doesn't need all the realism of modern racing games, this is a great diversion and, at least in my case, a great game to pick for "loser buys the beer".