Mario Kart 8 looks good, but I still don't like the way they treat gravity. It appears to work as if gravity always pulls you down against the surface you're driving on, regardless of its orientation. That means that steep downhills are only treated as small declines (the best illustration of this would be MKWii's Rainbow Road, where what should have been a vertical plunge right after the finish line becomes a normal raceway turned 90 degrees). The game seems to have some concept of uphill and downhill, but the angle of it doesn't seem to matter much.
Universal gravity, a proper weak one, would enable a lot more interesting jumps (high speed = epic jump, even on non-ramps), and uphills or downhills would affect the speed of your car to a greater degree. It would also look more realistic when you're ejected from the track (for instance when hit by a shell); you'd be tumbling down the hill instead of going up and down again as if you were tied to the race track by a piece of rubber. A proper set of physics wouldn't hurt the game. Inertia and universal gravity would make for some rather nifty crashes, at least.