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?