I am using Metacritic and its advanced search function to answer this most relevant of questions. Which game is the absolute worst, and thus far into my search I have learned something very important. The worse a game is the less likely someone will find the sheer will power to play and then review said game. Basically there are a few games at the bottom of the pile that were so bad that nobody could bring themselves to review them. Thus far the lowest end title happens to be.
M@M Kart Racing for the DS which got a massive score of 17 from Nintendojo.
"There are a thousand better ways for gamers to use their money instead of buying M&M's Kart Racing."
Damn that is one bad game, and yet not a 10 like what Varmint Hunters got a couple years ago. However that game was just a display in animal cruelty.