A good referee

Every referee will have a different interpretation of the rules book and what they think is and is not an infraction.

A good referee has a great understanding of the rules and to me doesn't apply the rules too loosely (so that the game is unfair) or too tightly. (So it becomes a whistle blowing competition)

A bad referee is an inconsistent referee. Those referees are useless and hurt games. Early on in a game an athlete should have an idea of how a referee will apply the rules. If a ref lets you get a way with things then you know that you have some more freedom while playing the game. If a referee is strict you know to be really careful.

Referees that fluctuate from strict to loose interpretation within a game are bad for the game.