I agree completely with your statement. Besides the piece by piece analysis of her work that supports that assessment, remember that Plath's life writings are essentially a journal of mental illness, and thus, there is no way they could not be intense, personal and disturbing. In reading her works, we are witnessing the step by step unraveling of a human being.
I do agree that Plath's poetry is intense and personal, but I do not agree that her works are disturbing. As mentioned before, Plath was a confessional poet. Her poetry was built around the traumas and tragedies in her life (as well as her own emotional/mental "issues"). I enjoy the honesty of her poetry and do not find it disturbing at all.
These are good adjectives to apply to Plath's poetry, especially deeply disturbing. Certainly when we think about the poems that address her relationship with her father, such as "Daddy" and "The Colossus," we can see the truth of these adjectives, as they are deeply personal and rather worrying in terms of the emotional vulnerability of Plath her level of self-disclosure.
Yes, certainly many of Plath's poems are highly intensely, particularly her well-known work "Daddy," which ends with the following lines:
There's a stake in your fat black heart
And the villagers never liked you.
They are dancing and stamping on you.
They always knew it was you.
Daddy, daddy, you bastard, I'm through.
In a sense, Plath might be called a kind of "dark Romantic," since her poetry is often stongly emotional but rarely in any celebratory way.
Sylvia Plath is usually categorized by critics as a `confessional` poet, a term meaning that she writes explicitly of intensely emotional personal experiences. The subject matter of her poetry ranges from the genuinely traumatic (suicide, hospitalization) to the minutiae of daily life (babies, bees, flowers), but she often uses horrific and hallucinatory metaphors to describe even ordinary objects. For example, in `Tulips` the flowers are described as blood like and eating the narrator`s oxygen. How much we wish to identify Plath with the narrator or protagonist of her poetry depends on whether we are aiming at psychological criticism and what we assume about the nature of poetic voice. Since Plath was a WASP, not Jew, and her father was not a Nazi, we cannot take much of the metaphor literally.
Many people do find Plath`s poetry disturbing; others find it shrill and melodramatic. Rather than judge the corpus as a whole, perhaps it is better to judge individual poems on their own merits, and not try to generalize about them. Plath has some very gentle lyrical poems as well as the more exaggerated ones.
Her nice effort ARIEL is also fits on your answer, Movements and feelings of a women while she was on horse back are too Intense, deeply personal.and quite disturbing.