Mario Kart has always been a prominent name in non-serious racers, but now it's even better than before!
The 4 new grand prix's are great fun - with some really well-designed courses
(Mario Circuit, Peach Gardens); and a few ones just for fun (Waluigi Pinball!). The 4 retro grand prix's are chock-full of nostalgia - and I was grinning with anticipation at some of my favourites from previous versions (especially Bowser's castle from the GBA - that course is fantastic.
The mission mode is another delightful addition, that really helps lengthen the game - together with the ratings going up to 3 stars (I finally got the top ranking on everything today!). They're really good for learning the game too, and the boss battles again have some great nods (especially to super mario 64).
The multiplayer is great fun, although it can be a little frustrating with some of the people who have practiced this to a ridiculous extent are zooming round the track. Overall though a fantastic addition that makes the game even more worth your while.
All I can say this is probably the most essential game for DS at the moment, and everyone should play it. If you don't have it, go and get it right NOW!