“We’ll go no more a-roving/ So late into the night,” Leonard Cohen sings on the opening track of his eccentric, challenging new album “Dear Heather.” But the underrated Cohen, who turned 70 in September, has continued to release album after album despite a failure to achieve widespread popularity or commercial success. His astonishing lyrical skill and the distinct ideas and themes of his work have remained largely constant within a musical landscape that has grown and changed with the times.

In its sound and content, “Dear Heather” marks the culmination of Cohen’s music career. Though the album is inconsistent, with several rough spots of experimentation, its high points are as great as anything Cohen has ever released.

As its affable title indicates, “Dear Heather” is a quiet, musing work. The cynicism of “The Future” (1992) and the bleak incisiveness of “Songs of Love and Hate” (1971) are replaced by introspective contemplation befitting an artist who has just reached his 70th birthday. In that respect, the album has an additional perspective of several decades as well as the weight of serving as a reflection on his own work.

Cohen rose to prominence as a singer-songwriter in the 1960s, after having already published two novels and one anthology of poetry in Canada. In 1967, Cohen moved to the United States to pursue a career as a folksinger. His first album, “The Songs of Leonard Cohen” (1967), was popular among college students but his music never caught on with the mainstream. His work has been characterized by melancholy and lyrics that resemble poetry. In 1996, Cohen was ordained as a Zen Buddhist monk; the album’s quiet reflection seems inspired by his religion.

Lyrically, “Dear Heather” is as strong as any album of his long career. Cohen pays tribute to his background as a poet by dedicating several songs to the people that influenced him, such as the Canadian poets Irving Layton and A.M. Klein, and F. R. Scott, once one of Cohen’s professors. The album even begins with a tribute to Lord Byron; Cohen adapts the poem “Go No More A-Roving” into a jazzy, relaxed song.

“There For You” and “The Letters” are Cohen at his best, with effective musical instrumentation balancing lyrics that are nostalgic, pained and newly aware of mortality: “Death is old,/ But it’s always new./ I freeze with fear/ And I’m there for you,” he sings on “There For You.” On these tracks, the melancholy quality of Cohen’s famously unmusical vocals — deep, coarse and monotone — are well complemented by longtime collaborator Sharon Robinson’s vocals to create a sublime beauty. Cohen’s chant, quieted to a barely audible whisper at times, is all the more haunting on songs such as “On That Day,” a response to the events of Sept. 11, 2001.

Cohen has tried, mostly successfully, to incorporate a number of musical styles and elements into his work. Recently, his albums have been characterized by a fusion of country and folk, with the continued use of the synthesizer sounds that were so effective in increasing the scope and magnitude of albums like “The Future.”

“Dear Heather,” though, overuses synthesizers and solo saxophones, and sometimes ventures into the gray area between quiet, unhurried music and cheap elevator muzak. In particular, on the tracks “Villanelle For Our Time” and “To a Teacher,” the music seems almost an afterthought to the admittedly fascinating lyrics. In “Villanelle” the sparse noodling on the synthesizer and horn sounds like half-formed ideas rather than realized music. Nevertheless, Cohen’s deep, chanting voice commands attention and seriousness, smoothing these rough experimental passages into one continuous whole.

The title track, however, is a bizarre, unsuccessful experiment that is perhaps the weakest song on the album. A repetitive and almost childish melody plays under Cohen and singer Anjani Thomas’s repetitive five-line chant. Cohen tries to achieve a certain effect with the repetition, but the result is difficult to listen to and out of context.

One wishes Cohen would stick to the kind of fascinating, unsettling beauty he proves himself so capable of on two of the last tracks, “Nightingale” and “The Faith” — the album’s masterpiece. Cohen’s and Thomas’s voices combine to give the song a haunting beauty, and its creative instrumentation and arrangement, which includes an enchanting violin solo, are gorgeous. The lyrics are nearly heartbreaking, filled with regret and pain. “So many graves to fill/ O love, aren’t you tired yet?” he sings.

Cohen’s words seem to look back upon his magnificent career; should this end up his final album, it will be a worthy coda. But the interesting and provocative “Dear Heather” indicates there is untapped potential that can yet be realized in years to come.