Casual Games = Water
Hardcore Games = Soda
For the sake of this argument we are going to assume there is a difference between what are called "casual" games and what are called "hardcore" games. And let's be honest, there is a drastic difference in a game such as Gears of War and a game called Wii Play. What I find interesting is the relation of "casual" games to a glass of water and "hardcore" games to a can of pop.
Water has a plain flavor that anyone can enjoy. Give a 12 year old child a glass of water and they love it; same goes for an 85 year old woman. Grandparents love water. Much like "casual" games, everyone can enjoy a tall glass of water.
Soda pop has a much more complex flavor when compared to water. It almost has an acquired taste, one that many older people do not enjoy do to the excessive bubbles (complicated controls) or the "it's bad for you" reputation (violence). I know not all hardcore games have violence but that is the common belief among non-gamers.

I am the type of gamer who loves both types of beverage (talking about games now). I own and love drinks everywhere from Dasani to Aquafina to Fiji (Brain Age, Wii Sports, Picross). But I also love myself some Mountain Dew, Dr. Pepper, and Sierra Mist (Halo, Gears of War, and Super Smash Bros). All of these drinks I can enjoy, a good beverage is a good beverage no matter the type or the flavor.
Mario Kart Wii is an interesting beast in regards to this beverage analogy because it is trying to appease both the water crowd and the soda crowd. This game to me seems closer to a
Propel Fitness Water, which I do not enjoy. There are certain things I do not like about beverages and one of the main ones is when you water down my fountain drink. I'm sure you have all taken a drink of your 7-11 fountain drink about an hour after you fill it up and the ice has begun to melt into the drink. It's nasty. That is how Mario Kart Wii tastes to me.
I can't quite put my finger on the reasons why Mario Kart Wii seems like a watered down version of the series but it simply tastes bad in my mouth. Could it be the lack of a co-op Grand Prix mode? Perhaps. Could it be the requirement that battle mode is team based only? Maybe. Or could it be the fact that it is impossible to be eliminated in Battle Mode because it is all score based? Good chance. There are simply no options, no complex flavors.
Even though they are adding an online mode it still seems to me that this is a watered down version of the series' past. Please explain to me why this is a delicious flavored beverage because I would like nothing more than to continue my love for one of Nintendo's greats, but it simply isn't happening right now.