In many respects, Solesmes editions offer a new perspective on contemporary liturgical praxis in the West, including the modern Roman Mass - see my review of the Gregorian Missal highlighting the impressive body of chants available for the modern Roman rite, including the replacement of the responsoral psalm with a proper gradual.The Liber Hymnarius similarly addresses the often bemoaned lack of proper chants for office.
As the book title aptly indicates, the corpus of Latin hymns for the office is provided with annotation. Since liturgical reform of the Roman books wisely jettisoned the revisions to the corpus of hymns applied by Urban VII, the hymns for the Roman office and the Monastic office essentially correspond, the only variance being in the hymns supplied for proper Benedictine feats not included on the general Roman calendar. One can, therefore, use this book for both Roman and Monastic observance, although I'd personally recommend Monastic observance.
As with most every hardcover "blue book" published by Solesmes, the binding is quite good. A sturdy hardcover, sewn binding, crisp printing, and quality paper. The paper seems a notch lower in opacity compared to Gregorian Missal, but this is not enough to distract or cause any problems with the text.
There are two major draws to the Liber Hymnarius: the Latin text and the chant melodies. There are, of course, a few voices that have argued that although the Latin text improves over Urban VIII's revision, the hymns are not a uniform restoration of the ancient corpus. There is some truth to this. In some cases a strict adherence to the most ancient text of a given hymn was not followed on the grounds that the repertoire of chant was based around later readings of the text. In other cases, new hymns were composed. For the most part, it is the later that sets off criticism. The West has endured a recent history plagued by the phenomenon of new compositions of mixed quality; this is almost a knee-jerk reaction to anything of contemporary origin. By and large ancient melodies were utilized for the chant and the new text retains fidelity to the monastic tradition.
The monastic propers add a layer of depth to the observance of the sanctoral, a quality that was lost amid the deep redaction of the Roman Calendar during the liturgical reforms of Paul VI. The sanctoral often reflects the history and experience of a community, adding layers to the narrative understanding of both origin and purpose. While the intention was to prune the general calendar to make way for local observances, it has to be noted that the monastic and religious orders had more success with this venture than most any dioceses.
As noted above, one can use this volume for either observing the modern Roman office or for following the Benedictine office. One will get more out of it if one follows the Benedictine office, either as codified in the existing schemas or adapted as appropriate. The Monastic office was fairly conservative with its "reforms", it also avoids much of the well intentioned but poorly executed pastoral liturgiology influencing the modern Roman books.
Regardless of the office one prays, the Liber Hymnarius is easily enough applied - and for those who have endured the selection of vernacular hymns utilized in the modern English breviaries, the corpus of Latin hymns and responses will be a much needed repose.
You can buy a copy through Amazon, of course. You can also order it from Solesmes directly, the preferred option - the monks have the more aesthetically pleasing website, and, frankly, do you really want to give Amazon any more money?