"It is death to mock a poet, to love a poet, to be a poet."
-Ancient Irish Triad, quoted by Robert Graves in The White Goddess.

I am reading Chapters in a Mythology by Judith Kroll. The important point that I am gathering from this criticism is that Sylvia is not a "confessional" poet because she is developing her own mythology that uses the disguised events and people of her life. She is not using the mundane or everyday events of her life to create surprising poetic connections.
This makes Ted Hughes' Birthday Letters and Frieda's Woorooloo and Fourty-Five seem all the more confessional because they both take real life events described very plainly and elevate them to poetic meaning. They both rely on our knowledge of Sylvia's life events to create thier meaning.
Kroll's analysis also draws an interesting parallel between the sculpture and painting of de Chirico. The world of the later poems resemble the barren and guant landscapes created by de Chirico. Also, both artist use the moon as a central image. Plath's moon is tied up with the cycle of womanhood, fertility, and the muse of creativity. Some of the poems such as "The Moon and the Yew Tree" become a new experience in her fresh descriptions of the moon's influence on the landscape she presents.