What exactly would you consider to fit in the category of "worst"? Do you mean in terms of difficulty to the point of the game not being interesting? Or perhaps you mean the quality of the story? Maybe the gameplay and mechanics didn't suit your liking? You didn't quite meet eye-to-eye with the graphics?

If I were to pick a game considering all of the above, I would probably have to choose (from my experience) Final Fantasy 13-2. Never have I ever been so lost in a game's "direction" than I have with that installment within the series. Although the controls were pretty clunky, I looked over that in order to pay more attention to the story and gameplay. It wasn't until mid-late game that I've noticed that the direction of which the game is suppose to put you in is a complete mess, really. It's one of those games where if you were to put it down for a week or so and return back to it, you wouldn't really know where to go. There's just a bunch of time gates here and there and everywhere... I almost feel like they were trying to put on a Chrono Trigger vibe, but failed miserably. And don't get me started on how ridiculous the DLCs were... and being expensive for no good reason. All-in-all, my experience with FF 13-2 started off positive, but later down the line became worse and worse and I knew by the time I had finished the game that I had indeed played a "bad" game, from my experience.