Summary: Fun racing game, the WiiU one is especially neat with supporting 5 players. Transformation mechanics are cool, although the cars are by far the best part. Framerate is pretty good, but suffers a bit when directly compared to Mario Kart. Sonic is definitely the more challenging game, with fewer random and rubber-banding elements compared to Mario Kart.
Summary: This game is great if you like racing games. I expected it to be a little more like Diddy Kong Racing (for N64) because you could use a car, hovercraft, or plane. However, the game kind of decides when you are going to change your vehicle - whenever you go through one of the glowing blue circles, your vehicle changes.
Summary: Sonic makes his debut on the WiiU platform with this game. Plenty of tracks and characters to unlock to keep you busy for awhile. This is a game that's great in off screen mode, but it obviously doesn't look as good as playing on your HD TV.