Sylvia Plath basically lacks the vision of the great poet. Her focus is narrow--- on the painfulness of her being. Lacking the strengths given by common sense and objectivity, she makes imaginary leaps which end with her landing on nothing. I'm especially referring to her comparison of her own condition to that of a Nazi victim--- which is so false, so empty, so extreme. Daddy is the ultimate poem of this type. Her:
                     
                          I have always been scared of you,
                          With your Luftwaffe, your gobbledygoo...
                          Panzer-man, panzer-man, O You---

                This is false, hysterical, out-of-control. It can lead her to write

                          Every woman adores a Fascist,
                          The boot in the face, the brute

                 which she doesn't believe.
                 She compares herself to a Jew:

                          A Jew to Dachau, Aushwitz, Belsen.

                  That is so false, so cheap, so easy. She doesn't know what she's saying.
                  Much of her work expresses little more than an all-enveloping disgust--- with herself, with others, with anything physical and real which therefore reminds her of life. It is suicidal verse, a friend of death, a kind of black mass. From Elm:

                          Love is a shadow

                          ...shall I bring you the sound of poisons?

                          I have suffered the atrocity of sunsets.

                          The moon...
                          Her radiance scathes me.

          Poetry like this reminds me of the work of the Jacobeans Webster and Tourneur. Yet there's a certain largeness and pity for others in Webster that Plath doesn't have. As for Tourneur, even he is bigger and has more light, more energy, more humor, more purpose, though his plays are nihilistic/about nihilism. But in a successful play, no matter how nihilistic, there are still people, settings, actions, energies, life. But some of Plath's poems are so airless, so claustrophobic, so devoid. No one, nothing, can enter these rooms--- husbands, children, would-be love, her art, nature, her own image--- without turning into a thing of disgust.
          In addition to which--- some of her language is quite below what a great poet writes:

                          Your stooges
                          Plying their wild cells in my keel's shadow,
                          Pushing by like hearts,
                          Red stigmata at the very centre,
                          Riding the rip tide to the nearest point of departure...

          The word choice in the above isn't the best. She's thrashing, her images don't cohere--- to the normal reader the above is, in fact, incoherent. A good bit of Plath's verse is, in fact, incoherent.
          At other times, her language is simply modern-flat, the time's standard issue.

          And now the yet.
          When I first read her poetry, years ago in Time Magaine's review of Ariel, I was floored by it. It seemed written in fire, not ink. It was so brave, so starkly powerful, so two-fisted, so totally un-academic. And, re-reading Ariel, much of it still is. And as for her vision--- well, it may, in fact, be small, but she has created a world out of it--- it may be a small world--- but there it is--- and very few poets of our time have done that. Whatever your vision is, artist, you should be willing to die for it. How few are. This one would, did. She was willing to die for her disgust. She was real.
How few poets are real. She was nearly mad--- in her last act she was--- yet honestly and coherently so.
            And now I come to the key, why her verse lives, where its power still comes from. Deny it as I did earlier, her vision of disgust links. We who live must feel it, if we can feel at all. Not always. Not suicidally. But sometimes. If we are human beings. She has taken our continent and made it her whole world, yes, but still, we and she have lived in the same place at times, and then she is our poet. If she can just find language strong enough, she can indeed write poetry of negative greatness. And, sometimes, indeed, Sylvia Plath does:

                            O love, O celibate.
                            Nobody but me 
                            Walks the waist-high wet.
                             The irreplaceble
                             Golds bleed and deepen, the mouths of Thermopylae.
                                                                                        ("Letter in November")

              
             That is great poetry. Even the half-incoherence of "Thermopylae" works--- we know what it means.

                              Let this eye be an eagle,
                              The shadow of this lip, an abyss.         ("Gulliver")

              All of "Cut" is amazing. Several other of her poems, whatever their extremism, seem to me to totally work at a very high level: "The Applicant", "Fever 103", "The Arrival of the Bee Box", a few others. In "the Applicant", Plath is great in a new kind of way. The wild humor of this piece! The incredible rightness of the language for this kind of vision. Its rhythm, its pace--- its command, its daring, its grip.
               Sylvia Plath is probably more an extraordinary poet than a great one. But, admittedly, let us be afraid to be the kind of person for whom she will be a great poet.