As an old Plath fanboy I found this post on bookslut wonderfully correct and beautiful.
There were two kinds of ancient Celtic poets: bards, who learned songs and stories and recited them, minstrel-style, and filid. The fili were visionary poet-magicians. Like bards, they memorized ancient stories and lore, and wrote eulogies and satires. A bard’s satire was just a poem, but a fili’s satire was both poetry and magic. It was a curse, and if a poet sang a satire about you, it would hurt you or sicken you. It was no small thing to anger, betray or disrespect a poet.
Sylvia Plath (1932-1963) was the premier satirist of postwar American girlhood, but that isn’t the only reason her work is so great. She was a lyric poet, unafraid of verse and the beauty, power and menace it can convey. We’re unlucky enough to live in an era when “no rhyming poetry” is a submission guideline for any number of bloodless literary journals, as if Plath and Eliot and Brodsky never existed. There’s a link between rhythm and power in poetry, and Sylvia Plath’s creepy nursery rhyme rhythms and refrains stay with you, viscerally, emotionally, like a comfortless lullaby in a frightening childhood.