I've seen The Importance of Being Earnest, so the wittiness is what I expected. He does lay it on a little thick, but the more I read the more I see it as cynicism towards how people think they know everything. I think Wilde's wittiness can be seen as something interesting to think about in its own right, or as a way to mock the character who's speaking.

The thing about realism in fiction is that it has to balance with entertainment value. And fiction has to make sense, unlike real life, so it can't be too realistic.