What makes a game good can vary from game to game. However, a few things go into making any game good. Clear, understandable rules are required to make a game good. If the rules don’t make sense or aren’t clearly communicated, the game can’t function properly. Also, the mechanics must reflect the metaphor and vice versa. A game with mechanics for fighting enemies wouldn’t work as a game about doctors curing a disease.
Some may say that a game must be fun to be good. However, even disregarding the subjectivity of what is fun, not all games must be fun. Depending on the game’s message, a game might be fun or not. Some more experimental games use lack of fun to great effect.