Death Tank Zwei is one that was so disappointing that I forget it exists. The Saturn version is one of the best shared screen multiplayer games in existence, especially when played with six or seven players.
They made the graphics into a mess, they spoiled some of the controls at bit, and worst of all they released it on the only console incapable of doing more than four players on one machine.
Nights Into Dreams, and its sequel Nights: Journey of Dreams.
Journey of Dreams actually has some amazing levels, and there's really good content in there... but oh, the voice acting, and... THE OWL! SHUT UP AND DIE OWL! If ever there were a game that needed all its story and interface ripping out, it's this one. I sometimes think that this could get a director's cut and be re-released in a fixed form...
Thankfully there's a nice remake of the first NiGHTS game which goes some way towards easing the pain.
Which games have you wanted for six, ten, or even more years before being faced with something horrible?