Longman has written a solid commentary on the Song of Songs, interpreting the various metaphors and euphamisms with insightful clarity, and without falling into the eisegetical pitfalls of many other scholars who have found all sorts of ingenious references, sometimes even to activities forbidden in other parts of the biblical canon. I think he does, however, press the "initiative" role of the woman too far when he understands it as evidence for egalitarian marriage in Scripture.
In his introduction, he convincingly argues for what he calls the "natural" interpretation of the book, that it concerns human sexual relations, over against the more traditional analogical interpretation. He still finds room for a typological application to Christ and the Church, since marriage is the primary biblical metaphor for God's relationship to His people. I do wish, though, that he had brought forward more suggestions on how to draw such typological conclusions. He also argues convincingly that the Song is ananthology of loosely connected poems without any overarching narrative.
The book is highly informative without being overly technical, as other volumes in this series are. I can wholeheartedly recommend this book to any seeking to understand this often-neglected book of biblical wisdom.