If you want a good kart racing game, save your money and wait for Sonic and All-Stars Racing Transformed to go on sale. LBP Karting is fun, but the racing itself is incredibly shallow. Sonic is one of the best, if not the best, kart racing games I've ever played.
As soon as I see Sonic Transformed for $20 for Wii U or 360 I'm getting it. That's what I've been waiting for.