I happened to pre-order from GAME, and the pre-order arrived at my door in a shiny red Royal Mail van this afternoon, so I have been able to play it before it's technically released in the UK!
And what a game it is! The new tracks are pretty much all simply amazing, with some real classics dotted throughout the cups, and the retro tracks look really good too - especially with the graphical upgrades for the DS and GBA ones which really work well! Everything looks crisp and tasty and the game plays really smoothly with a great frame rate.
The real decider is the "Wii Wheel" - it comes free with the game and your Wiimote simply slots into it. It is very sturdy and feels good in your hands, although does take a little getting used to. According to my stats, I've used the Wheel 53% of the time, with the other 47% being used by the old GameCube controller, which does seem to feel more 'natural.' That aside, the Wheel is very good, much better than I expected.
Moving to online, the modes supported are wide and varied, and they take up to 12 players on one race. There isn't much waiting in-between races and if you have to wait to join a race then you can watch the progress live. Track choices are made through voting and there is absoultely NO LAG AT ALL. Which is awesome, especialy in a 12-player karting melee! Battle mode is also online, although has been ruined; the only bad point of the game.
This game is amazing. Buy it tomorrow morning ASAP!
9/10