Mario Kart 8 does not exactly turn the series upside-down.
The Mario Kart 8 demo definitely has an air of familiarity to it. You can select one of 12 returning characters, choose a kart or a bike, and use the same control options as in Mario Kart Wii using a Wii Wheel or Wii Remote, or play with the GamePad using the control stick or motion controls. Returning from Mario Kart 7 are the glider and underwater racing.
The biggest change: a sort of hover-kart/bike transformation that allows you to cling to walls or ceiling. This transformation is triggered in specific sections of a track and the player has no control over it beyond the choice of taking the occasional alternate path.
The trailers for the game make racing on walls or ceiling look disorienting, but during actual play, the camera is tied to the kart in order to keep the controls consistent. But while this allows the game to remain playable and simple, it also means this new mechanic lacks "oomph". Since the track remains under you at the bottom of the screen at all times, racing feels the same on whatever surface you happen to be on. The main impact is having to look for shortcuts and alternate paths on the walls.
Beyond that, the tracks are wide to accommodate 12 players when racing online and the game looks very much like a high definition version of the Wii game. There are perhaps more details that are easy to miss while playing, but are nice touches when looking at someone else play. For instance, one of the tracks takes place in the streets of a town with a European air to it, and ads for Galaxy Airlines and shops such as "Mario's Workwear" help add some character to the place. The other tracks include a Ghost House with no real surprises to it, and what I can only describe as a generic Mushroom Kingdom circuit.
The lighting has gotten a nice upgrade and fireballs light up and explode beautifully, but that is about the most noticeable graphical improvement. The framerate is fast and steady (at least in split screen, two player mode), and the art style remains simple and familiar. There is no way for one player to use the full TV screen and the other to look at the GamePad in the demo.
With the most refreshing-looking addition to Mario Kart 8 being less of a game-changer than it appears, those looking for a fresher Mario Kart experience will be disappointed, while those who are just looking to do tricks and pop wheelies in HD are getting exactly what they want.