Jean Valentine's poetry career began inauspiciously. For ten years she submitted her writing to publications, but each time met with rejection, perhaps due to what Times Literary Supplement reviewer Jay Parini described as "the stripped, unyielding quality" of her work, a quality Parini maintained "will admit few and discourage most of her readers." Finally, in 1965, Valentine's last-minute entry in Yale University's Younger Poets award won her both the prize and publication of her first book, Dream Barker, and Other Poems. She has since established herself with the same obscure, suggestive style that characterized her first volume. "Valentine's audience has always been small but enthusiastic," wrote Parini, "which is the sort of response one expects for a poet whose work is dense, almost hermetic, yet striking and intense." According to Praxis contributor Crystal Koch, who reported on a 1997 poetry reading attended by Valentine that was held at University of California-Davis, Valentine's audience found her work to be appealing and thought-provoking; they appeared to feel connected to the "vivid images" that she presented in "a simple manner."

Koch also commented of Valentine's work that one of the poet's strengths is "her ability to portray the down-to-earth quality of [her subjects]." The people and life on Saint Lucia Island and in rural Ireland are among the subjects she profiles in Growing Darkness, Growing Light, her 1997 collection. Koch related: "The poet expressed an empathy toward her subjects and a desire to convey their struggles, their attitudes and their feelings." The pieces in the volume "are marked by moments of brief intensity," stated a Publishers Weekly reviewer, who went on to declare Valentine "a commanding poet" and Growing Darkness, Growing Light "one of [her] best collections." Do not read Valentine's work as "straightforward logic," warned Barbara Hoffert in a Library Journal assessment of Growing Darkness, Growing Light, for her "poems are like little drops of pure, unfiltered feeling."

In the New York Times Book Review David Kalstone described Valentine's unique language: "Miss Valentine has a gift for tough strangeness, but also a dreamlike syntax and manner of arranging the lines of . . . short poems so as to draw us into the doubleness and fluency of feelings." Paul Zweig claimed in the Village Voice that one problem with Valentine's dreamy style is "diffuseness. The impressionistic play of images tends, now and then, simply to trail away; to unravel, without any underpinning of form. When this happens, poems become flat, indecisive." However, Zweig had praise for Valentine's ability "to unresolve the reader's mind, to peel away its armor of opinions; to make it solitary, vulnerable and attentive." Kalstone admitted a similar reactive response to Valentine's poetry: "She does not 'see and take' so much as initiate the reader into very private feelings."

"Valentine's lifelong identification with poets like Rilke and Mandelstam is a key to understanding her own dreamlike but fierce stance," explained Carol Muske, reviewing Growing Darkness, Growing Light in Nation. Valentine, who deserves to be given more considerable and considered attention according to Muske, is "a writer of deep-image, projective verse." Muske added: "What has distinguished her verse in the past is its refusal to be anything other than what the 'conscience' of her poetic vision has sanctioned. Thus, her poems are brief, unswervingly drawn to the oracular. Yet nothing is 'enhanced' or self-consciously mythic. . . . There are no unessential details, everything is given equal moral and aesthetic weight, as in a dream." Muske concluded that "the poems in [Growing Darkness, Growing Light] are indeed dreams, but precise dreams of waking: startling junctures of the abstract and the carnal."

Referring to Valentine's "dizzying, elliptical but seemingly effortless coincidence of emotion and idea within the confines of the pared-down lyric," Muske acknowledged that "Valentine's style definitely leans to the cryptic." However, declared the critic, "[her] mastery of the form, the deep image, [is what] keeps these unlikely barks afloat." Despite such an assessment, in a review of Valentine's 2000 poetry collection, The Cradle of the Real Life, a Publishers Weekly critic remarked that Valentine's "command of form can't always equal her feeling." As such, concluded the reviewer, The Cradle of the Real Life is both "harrowing and frustrating." In her quest to compress, commented the critic, she creates "ostensibly completed poems and series read like notes for poems not yet written." Ellen Kaufman more optimistically promoted Valentine's 2000 volume in Library Journal, praising The Cradle of the Real Life as a "mature collection from an important writer" who gives "spare form imbued with spirituality." Although "filled with sadness," remarked Kaufman, The Cradle of the Real Life "is a book of much joy."