15: 1988-1994 Ford Tempo
Speaking of compact cars that never reached the heights they could, the Tempo is another such questionable model. Ford was looking to compete with the Chrysler K-Cars and so the Tempo hit the market. The design of the car was compact and there was a lot to like about it. The fuel economy was better than compact cars that came before it and initial consumer response to the new model was promising (via The Motor Digest).
Sadly, the same sort of problem settled into the Tempo in the form of reliability and build quality issues that plagued the car. Consumers were finding better deals from automakers like Honda and Toyota. The Tempo cost Ford millions to develop and send to the market, only to cost the company the same amount of money.