Uses of Language I Don't Get

From John Lahr's New Yorker review of the current revival of Sweeney Todd on Broadway. In the sentence below he discusses a benefit of the very abstract staging of the classic musical (bolding mine):

"In this production, which sheds the eggy trappings of naturalism, even the star-crossed young lovers, Anthony (Benjamin Magnuson) and Johanna (Lauren Molina), who usually come across as ninnies, take on a refreshing, compelling sweetness."

Eggy? What in the world does that mean?

Until Whenever