I haven't read the other posts, but I thought I'd chime in.
I wasn't planning on getting this game, due to the overall lack of gaming in my life. The GC and N64 versions were OK, and the wheel just didn't excite me. After seeing the review posted by Gametrailers, I really thought this was the lamest of the series.
Well I did get it, I had credit at EB, and was greatly surprised. The elements that they added are great. The trick system, although super shallow, adds a lot to the game. It adds two great elements to the game. One, it's gives you the extra edge to take the lead, or keep the lead. Two, takes away from the monotony of racing. One of the main reasons why I didn't like the N64 and GC (although I did play them through) ones was because I felt the transition to 3-d added too much space (another dimension, duhhh) but they didn't fill that space.
*thinks of Wario Stadium N64, boring, wiiiiddee track*
The added jumps and tricks in MK Wii fill that extra space nicely. Everything is more dynamic, and exciting to play. You can plainly experience this when you play the lower cups (retro stages) compared to the new tracks, the new tracks are super dynamic, with crazy aerials, terrain changes and excitement with every turn.
Things that I thought were a bad move by Nintendo, like taking away the drift dash maneuver (clicking the analog stick back and forth) "dumbing down gameplay", didn't really affect the game experience, it kind of makes me think of the "old system" as superfluous. I'd like to think it as streamlined, not dumbed down.
Everything in this game just feels faster. The extra mini boosts, and the wheelies on the bike, all nicely added features. I can't say the same for Double dash featuring 2 racers. Your thumb is always on the move planning ahead for drifts and jumps.
One thing I need to comment on is the items. There seemed to be complaints about unfairness, but for the most part, I don't see a problem with them, when you stick every drift and get every mini boost. I always end up at first. I've played through everything in 50 & 100CC, flawless. Maybe 150CC is insanely hard or sumthin, but I'm up for it.
I tried the wheel on one circuit, it was hard. It would probably be fun if others were all holding wheels, but playing alone, I choose the Wavebird (Nintendo Bring it back!) Which reminds me, pressing down on the analog R don't make you drift, which really threw me off ( I hope I'm talking about the right game...) in the beginning, you have to press it all the way down, but like now I don't even notice, that's why I questioned if this is the right game (but MK has pretty much the only game i've been playin so it has to be). I'm pretty sure in MKDD you didn't have to press all the way.
Well anyways, partly because of my low expectation and a couple reviews, I really thought this game was going to be weak. But now I think this is the best of the Mario Karts. The tracks are awesome, the features are amazing, online... I keep getting kicked off, but I think that's a router problem. Well online is fun when I could play. If you have a Wii, this is a must have.