Mario Kart is ok but they're all the damn same. IMO (and I'm probably going to get flamed for this) they should make one final mario kart for the Wii U, make it the last ever, go all out and include EVERY track from past mario kart games, EVERY piece of music, and EVERY character, also including brand new tracks, brand new music, and brand new characters (more or less the entire mario rosta, koopalings, the lot!) They should make it the ultimate mario kart game and make it the final in the series, because IMO it's ran it's course.
However, this will never happen, and we'll see many more MK games yet as it's still making nintendo a lot of money, but those are just my personal thoughts nonetheless.