I've bought my share of bad games, but most of them I bought cheap and only half expected to be any good. The worst ones are those that have you expecting greatness and then turn out to suck just as bad as those in the bargain bin.
Gungriffon Blaze = biggest disappointment in an unknown game for me. I love Armored Core, and this looked like it had similar gameplay. Unfortunately, I couldn't play more than 5 minutes of it because the damn sticks were reversed. There should be some kind of law that the left stick will always be for movement, and the right for camera/turning. Even worse, the game was stuck in first person so I couldn't even look at my mech or see where it was going.
Metroid Prime = the single biggest disappointment in a game ever that I can recall. I knew this wasn't going to be like the 2D Metroids and that it was styled after an FPS with more platforming than usual for them, but for the love of god WHY did it only use the left stick?! The game has the same controls that FPSs had on the N64, which means that you can't aim and move at the same time. Now I realize that the game had an auto-target feature, but to me that ruins any fun an FPS can have. I mean, what's the point of playing a shooting game when you don't have to aim? Aside from that, A and B were also reversed from everything we've come to know and love. The worst part is that I really really wanted to like this game, since it looked great and the environment was interesting. I was able to play through something like 1/3 of it, but once the enemies got dangerous there was no fun way to fight them. You either let the game aim for you while you run back and forth mashing A, or you aim yourself while standing there like you're a f***ing gun turrent. One thing I DID like was the morph ball, and whenever my friends wanted to fight me in Prime 2 I would fight ONLY in ball form. Surprisingly enough, you can actually put up a good fight with the ball alone. Sorry if that read like a review, but I'm still in shock even now that nintendo had a controller with two sticks and didn't let you use them properly.