For the sake of this thread, I'll define unpopular as "not liked or heavily flawed" to make this easier. Cult classics don't count.

I would recommend Evil Zone, I love this game, and it is truly terribly. There are bad fighting games and then there is Evil Zone where the controls are overly simplistic, the A.I. is horribly cheap, and the story... oh god the wonderful cheesy story and cast... I almost want to play it now.