This is not an analysis of Rossetti's poetry but an opinion piece.
What is it that makes Rossetti so uninteresting as a poet?
Perhaps the sheer volume of her poetry drowns interest? But Dickinson, prolific as she was, never bored me.
Is it her prosaic use of language? Perhaps. But Longfellow used language just like hers and wrote better poems. Longfellow invites thought; Rossetti, hardly ever. She does not have Dickinson’s knack for sprinkling her poems with unexpected or unheard-of devices and word-plays—so despite her ability as a storyteller, her words hardly ever invite her readers to question, to ponder, or to debate.
Is it the lack of variety in her verse? She used many different rhyme schemes and meters, but they always seemed more or less the same. She drones through the volume at the same pace, in the same voice. She is too predictable.
Is it her choice of topic?—invariably some lament, or introspection, or ballad, or didactic or religious verse. Dickinson was at times introspective or religious; Longfellow wrote ballads and didactic poetry; but there is this about their work that Rossetti lacks: a poem’s nearness to or ability to access the heart (emotion) or the intellect (reason), sometimes both (and then it is a masterpiece):
In terms of the heart, its ability to evoke emotion, by means of
addressing or reminding the reader of a previous experience (nearness);
arousing a certain emotion, e.g., sympathy, patriotism, horror, that was not already linked to a specific experience (ability to access).
In terms of the intellect, its ability to engage reason: to evoke thought, question, doubt, faith, by means of
confirming something that has already taken root in the intellect or has been suggested to it in the past (nearness);
presenting something new which raises further questions and may possibly be accepted (ability to access);
stimulating it by means of the discrepancy between a previous thought or belief and the thought or belief suggested in the poem (ability to access).
Rossetti’s poems hardly ever do any of these things. At best, some of them occasionally arouse a faint echo of an emotion, which is probably why her poems are not memorable. When I think or speak of a poet whose poetry I have read, there is usually one or two poems that come to mind; when I think or speak of Rossetti, there is none. If I were called upon to give an example, I would probably say “Goblin Market”, not because it is interesting, not because it provoked thought, not because of anything except that it is often mentioned in one-paragraph biographies of Rossetti; rote repetition left its imprint on my mind, or I would have forgotten it just as I forgot all the other Rossetti poems I’ve read. Like most of her other poems, it has no voice to speak for itself.