IGN published a detailed review and a video review of the upcoming Mario Kart for the Nintendo Wii (Amazon).

Quote from the review: "For the first time ever on a Nintendo console, the online portion trumps the single-player offering, and we'll explain why. Both 50cc and 100cc races are fine in Grand Prix, though the exclusion of the Mario Kart 64-like cooperative two player GP is a serious misstep in our opinion -- you can certainly go in and create your own GP competitions, but they work separately from the normal GP cup progression.
Mushroom Cup is a bit boring, Flower Cup starts to mix things up with some decent track design, Star Cup really starts to take off with some superb levels and true innovation, and a Special Cup that rounds things off with one of, if not the, best Rainbow Road tracks in franchise history."
Read the full review and see the video on IGN.

Mario Kart for Wii ships in 6 days on April 27th. Pre-order now on Amazon.com.