This one is by far the hardest to beat. Jesus Christ it's nearly impossible to finish ONE Grand Prix without losing 2 out of 4 races to blue shells or POW blocks. Some of the best Mario Kart tracks are in this one though, like Coconut Mall, Mushroom Gorge, and Koopa Cape. This is the last Mario Kart game where you unlock characters and karts through certain objectives, which gives you plenty to do. The most dumb fun Mario Kart game.
There's not really much to say about this game that hasn't already been said. Definitely one of the better Mario Karts, with a mostly great selection of new tracks and the choices for the retro tracks are much better than DS, arguably. Quite a few notable innovations like bikes, new items, the trick system. However this game DOES have it's share of issues, despite how much I love it. Going back to bikes...yeah, bikes. I know it was their first try but I think they're a bit unbalanced, let's be honest and say 90% of players use bikes because somehow Karts aren't nearly as good (it's in the title Nintendo, what the hell). The battle mode also isn't quite as fun, the character selection isn't bad but there's some questionable picks (enough of the baby characters, baby Mario and Luigi are enough for most people, also nobody plays as Birdo). Also I personally do not think character stats were a good idea, since it gives no incentive to play as anyone except the ones with the best stats (You know what I mean, Mach Bike Daisy and Flame Runner Funky Kong), it seems to kinda waste the franchises colourful cast. Other than that it's a very solid entry with a good variety of tracks, vehicles and characters.