That Mario Kart has gotten some middling scores before as a matter of course is a valid point to bring up.
Though it makes me consider that, on the whole, video game criticism does poorly / tends to be hypocritical about a certain category of game. Basically, the "breadwinner" game. Games like Mario Kart, or Call of Duty, are "breadwinners". They don't really strive to the lofty goals that intellectual (and pseudointellectual) Game Thinq (tm) likes to pontificate about. These games tend to be "stale" by the standards of whatever is the latest trend in progressive or 'artistic' game design. But they're games made to serve a specific purpose. They often perform their workmanlike role in a very refined manner, in the case of the longer running series. Let's face it... by this point, Mario Kart or CoD are down to a science.
But the hypocrisy tends to come in that games like Mario Kart, or Nintendo's audience in general, are not "cool" by the standards of 20-30 something males who are fully jacked in to the cutting edge of the gaming scene. Gritty shooters and the like, ARE cool.
So, I think you're much more likely to see CoD get a pass year after year, but games like Mario Kart get derided for being old and stale, with a "who plays those anyway?" subtext pervading the reviews.
From a perspective of actual critique, there's no reason to give two different games a different degree of leeway just because you're heavily biased to find one cool and one lame. Certainly, state which one you like more. But don't pretense to dock one of them for being "stale" in all the same ways your favorite game is also stale.
Like I said earlier, most game writing confuses critique with taste.