The 3 main genres of inspector calls are a well made play, morality play and crime thriller
A morality play questions personal morals (what one believes to be right and wrong) and also leaves the audience with a message. The main message portrayed in AIC is to accept responsibility for your actions
A well made play often has a cyclical structure. This could also be metaphorical to the idea that if the Birlings do not accept responsibility for their actions that the cycle will repeat until they do