Poe's fourteen lines begin as a love song to a place and end as a curse on it. The speaker greets the island of Zante the way a lover might greet a beautiful woman: "Fair isle," bearer of the "gentlest of all gentle names." But the sight of it does not simply delight him. It makes memories "awake," and what wakes is grief, centred on a "maiden that is / No more." The poem is about how a landscape can be ruined by what we have lost in it. The lovelier the place, the more it hurts.
The first eight lines build this slowly. Four times Poe starts a line with "How many," and each time the nouns and adjectives slide further from the light: "radiant hours," then "departed bliss," then "entombed hopes." In three phrases we go from sunshine to the grave. The fourth item, the maiden, is the one that cracks the pattern. Poe breaks the sentence across a stanza line so that "is" hangs alone at the end, and "No more" has to wait on the next line. Her absence is built into the line break itself.
From there the poem is ruled by that phrase. "No more" appears five times, in italics for most of them, and the speaker calls it a "magical sad sound / Transforming all." The word "magical" matters. The island's name was a gentle sound in the first line, and now a sadder sound has overwritten it, like a spell cast over the first. In the lines "Thy charms shall please _no more_– / Thy memory _no more!_" the phrase starts to replace the rest of the sentence. The speaker is giving up even the consolation of remembering. In this poem memory is the thing that does the damage.
The sound of the verse helps. The lines are mostly iambic pentameter, with alternate lines indented. The rhymes (flowers/hours, take/awake, bliss/is, hopes/slopes, sound/ground, more/shore) follow the pattern of a Shakespearean sonnet: three quatrains and a couplet. Poe prints it as eight lines and six, though, and the real turn comes early, at the break around "no more upon thy verdant slopes." After that the language darkens. "Verdant slopes" becomes "Accursed ground," and the line "Henceforward I hold thy flower-enamelled shore" runs longer than its neighbours, as though the speaker is overloading it. "Enamelled" is a telling word. Enamel is a hard, glossy coating, so the flowers sound fixed and ornamental rather than alive. Judging by the imagery, the island has already become something like a decoration on a tomb.
The ending is the most interesting part. After pronouncing the island accursed, the speaker cannot stop praising it. "O hyacinthine isle! O purple Zante!" is pure colour and tenderness. Then comes a final line in Italian, in quotation marks: "Isola d'oro! Fior di Levante!" ("Island of gold! Flower of the Levant!"). The quotation marks make it sound like a stock phrase of praise, one the speaker half-remembers and cannot help repeating. The couplet's rhyme of Zante with Levante lets the name return, musical again, in the last two lines. The curse is real, but so is the love beneath it, and the poem ends with the two tangled together.
Its significance lies in how much it does in so little space. It is a miniature of a preoccupation that runs through Poe's work, the death of a beautiful woman and the mourner left behind. The woman here is never named, and we are told nothing about her except that she is gone. That restraint lets the island carry all the feeling. "No more" is also a close cousin of the "Nevermore" in "The Raven," another poem in which a single negative phrase tightens around the speaker. "To Zante" shows the idea in its simplest form: a beautiful place, a lost person, and one small phrase that turns a paradise into a place the speaker can neither bear nor stop loving.