MarioKart has always been the only racing game I've bothered to play-- driving is just not as fun when you're not hurling ridiculous weapons at your enemies. I've been playing since the N64 version, and while I still think DoubleDash might be my favorite, the Wii version is pretty fun. I like the option of bikes, but I'm still not sure about the Wiimote controller... it's way too touchy for me to get comfortable with it. I still only play with the old GameCube controller; I feel like it's easier to handle.
My favorite part of MK Wii was the nostalgia tracks.

I love seeing the old N64 and SNES tracks updated and playable again. Makes me feel all warm and fuzzy again without having to actually deal with the old-style controllers.
The Wii game IS much harder than the others, though, mostly because they bump the AI handicap up to crazy levels. Essentially you HAVE to build up as much of a lead as possible, because on the 3rd lap you will probably get bombed, blue-shelled, and lightning'd at least three times. In a row. Right before you hit the finish. It's more than a little broken. But still a good game, I think. :3