There is humor and representation of polite and not-so-polite Victorian society. It is all quite realistic. The woman's main objective in this society was to land a wealthy husband, and this is, in part, the focus of this play. It is a very realistic portrayal of England during the Victorian era.
This play is realistic because it is a reflection of the Victorian London society, right as it was happening. The main characteristics of this very shallow and elitist period of history were clearly manifested in the play: Hypocrisy, elitism, moralism, differentiation of classes, snobbery, the fight to get to the upper crust of society, and the false imagery of grandiosity that the upper classes often promoted the way celebrities would do these days.
It is also realistic because Oscar is "in it"- He added the figure of the Dandy (Algy) as the overdressed and overindulgent Victorian gentleman (who we know is also broke and totally shallow), as the catalyst of change in the story (not to mention, one of the funniest)
The non-realistic aspects of the play occur thanks to the characters. Cecily keeps a diary of her imaginary relationship with a man named Earnest, and goes as far as getting engaged and breaking off the proposal.
Algy has his imaginary sick friend Bunbury whom he "visits" each time he wants to leave the country.
Jack has his imaginary brother, Earnest, who is wicked and whom he also "visits" when he wants to go to the city.
In all, the context in which the play occurs is quite realistic and representative of the society it mocks, whereas the characters, and their stories, display the most unrealistic characteristics, but it is all part of Wilde's style.
The Importance of Being Earnest is a Victorian satire that pokes fun at Victorian morality and social order. The double life of Jack in an effort to cover up his unacceptable behavior while in London is used against him by Algernon who takes on the identity of Earnest, Jack's alter ego.
Bringing Earnest to life as Jack's brother creates a comic situation where Algernon, an individual who also escapes with the use of a fake friend intrudes on Jack's life, this is a bit of a farce.
When Algernon arrives at Jack's home and falls in love with Cecily, it is a little hard to believe, especially because Cecily has already decided that she is going to marry Earnest, because she loves his name. When Algernon decides that he will be Earnest for her because he loves her, this is real.
Also realistic, is the idea that men in the Victorian era, in an effort to protect their reputations and their families, used fake names when they visited the city for a little freedom from their country estates.
Realistically, there is also a discussion of the separation the classes with regard to Jack and Gwendolyn. Victorian society had a particular social order and Jack is not eligible to marry Gwendolyn because of his status below her in social rank. But then, his real identity is revealed, that is unrealistic.