Australian theologian Peter O'Brien is a highly respected Pauline scholar who (in addition to this book) has also written commentaries on Colossians/Philemon and Ephesians, in addition to books on the Biblical theology of mission.
This commentary on Philippians is part of the New International Greek Testament Commentary series, a series that places a heavy focus on the original Greek text of the Biblical book in question and use insights gained from this linguistic/grammatical study as a launching point to comment on theological and historical content.
The structure of this book does not differ much from other Biblical commentaries. Several pages of introductory material (e.g. questions of authorship, recipients, major themes, outline) are followed by the commentary proper: a translation of the pericope, notes on textual criticism, and extensive remarks on the pericope. What sets this commentary apart from others is 1) the above-mentioned emphasis on the Greek and 2) a high degree of interaction with other New Testament scholars. This reader especially enjoyed the emphasis on the Greek--not because I have an intrinsic love of the languages (I don't!) but because O'Brien thoroughly lays out and defends his translation, then uses this translation-defense in order to draw out theological/practical/Pauline remarks. As he does this, he often lays out the arguments of other scholars and points out the pros and cons of each--not in a way to set up straw men, but to show why one particular choice is the best among plausible explanations. The end result is that I have much confidence in and respect for O'Brien's conclusions.
O'Brien approaches Philippians from a conservative perspective. He comes to the conclusion that the entire text was written by Paul (there were not redactors), that the recipients were the Christians at Philippi, and that the four major purposes in writing the letter were 1) to thank the Philippians for a gift he received from them, 2) to urge them toward greater unity (as it appears there was some conflict among them), 3) to encourage them to stand strong against a group of opponents from outside the church (who are trying to pull the Philippian Christians away from their Christian faith) and 4) to urge them to rejoice in Jesus, no matter what their earthly circumstances may be.
O'Brien's writing style is surprisingly conversational--I say surprisingly because it's difficult to come across as conversational when words and phrases like epexegetical, hapax, hortatory conjunction, and aorist indicative passive are used. When O'Brien remarks on the non-grammatical aspects of the text, his comments most often gravitate toward history, the personality/style of Paul, justification, sanctification, eschatology, and Christian unity. Absent or downplayed are the sacraments, vocation, the Holy Spirit, the doctrine of Scripture, and missiology (which is surprising to me considering this is one of his major scholarly pursuits).
In all, I recommend this commentary most highly for those who are have some background in the Greek. If you're concerned about the strength of your language skills (as I am), don't be intimidated. While it is based on the Greek, it is accessible while it remains scholarly and practical.