Here's the thing: Loved the tracks, loved the tricks, loved the bikes, loved the Wii Wheel, loved the graphics (by which I mean they weren't that bad). The only problem... four extra racers. It's not that there's more Blue Shells, etc., per se; it's just that there's more racers to use said items when they're programmed to suck. In a "normal" racing game, more cars is fine, but in Mario Kart, it transforms what was once a kind of luck-based racer into a full-out roulette wheel on... er, wheels.
Also, pretty much all the new characters were really stupid. Funky Kong must die.
When it comes to Mario spin-offs, I don't think anyone at Nintendo ever even thought the words "less", "is", and "more", in that order, at any point.