The games: Karnov, Rygar and Robocop
As much as we've ripped on the other games, at least they made an attempt. The effort was clearly put into the game itself, not the endings. Cartridge limitations made endings an afterthought for many developers. But these three, and many just like them, didn't even try. Karnov up there, also seen in Bad Dudes, is possibly the best of the worst. Congratulations!!
Rygar was a behemoth. Tackling that beast back in the day meant sacrificing a ton of your time, all for a tiny rainbow and then a brief description of how great everything is now that Ligar is dead. It's on par with the original Zelda ending, except the latter gets off easy, thanks to the heart-exploding intensity found in Death Mountain.
Robocop simply tells you to behave. You hear that, kids? Stay out of trouble. Do something constructive, like watch a viciously R-rated movie about a police officer who's brutally shot to pieces and rebuilt as a company-owned cyborg. Watch him rip the piss out of petty crooks and blast an old man out of a skyscraper. Watch him painfully realize that he was once man but is now a soulless abomination that eats baby food. That's wholesome entertainment for everyone.