I would say that most everybody who names a popular title (Such as COD, Halo, Final Fantasy, Half-Life, etc.) lacks a distinction between bad games and games not in the player's taste. Can you name to me any portion of those games you would call "Infunctional"? I happened to like MW and MW2, even if the story is kinda rediculus for the second. WaW has a very boring and predictable storyline and BO (in progress of playing this one right now) is very hard to follow (FFXIII has this problem as well). But functional? Certianly. You shoot and kill stuff, the game works fairly well dispite usually having issues with pacing gameplay. Halo? Clichie doesn't begin to describe the storyline, but it's definetely very functional as a game.
That being said I have to agree with the sentiments of someone before me who said "[If this is the worst, I'd love to see what you're playing.]" That being said, perhaps limiting scope would have helped this topic more, such as 7th generation systems or games of the last decade. Limiting this thread to only games I have played the winner is "Onechanbara: Bikini Samurai Squad" (Xbox 360). The obvious sexual pandering I overlook in games simply because I just don't care enough about it and it's not what makes this game bad. Anyway, the game has engine issues from the word go causing this weird ripple effect when the game is glitching. Secondly the game is very stiff with it's combo system requiring exact and split second timing to pull off combos past four hits or so which frankly I do not have since I stopped playing fighting games. But combine that with a special move you need to do in order to kill two paticular enemies and hours of spending time in the same place with said one of those enemies being unable to pull off the combo makes this game too infunctional to be worth any more of my time.
That being said, I think maybe I should start a thread saying "the least functional game you have played".