To start this off, let me give you some examples.
Pinball Graffiti, a pinball game for Sega Saturn where you could see from the ball's perspective in one mode.
Cybermorph, infamous Atari Jaguar flight game where your ship could change shape.
Banjo-Kazooie: Nuts and Bolts. Killed the Banjo-Kazooie games, but the vehicle building would've worked for brand new characters.
Why am I talking about these? These are three good ideas that were wasted in bad games.
What are some bad games you know of that had at least one good idea?
Some days I just blow up.