Davenant has two goals in his commentary on Colossians:
1) to fully and clearly exposit the text;
2) to fully and clearly refute the best Catholic expositions of the text.
He meets these two goals admirably, even if many people will be put off by the length of his commentary.
There are many Bible commentaries out there, so instead of focusing on aspects that are fairly common to them all (at least to all of the good ones), I'll focus on some things unique to Davenant:
1) The original publication was done in Latin by the Anglican Bishop of Salsibury John Davenant. This version was translated with notes added in 1831, so the language does not read with the regular density of a Puritan book. In fact, I was a bit surprised at how clear and simply the prose was, given the age of the book and the fact that it was in Latin.
2) In a sense, this is both a commentary and a treasury of the thoughts of the church fathers on the ideas found in Colossians. In arguing against the Catholics (specifically against the most recent and thoughtful Catholics available to Davenant: namely Bellarmine and the documents of the Council of Trent, along with several less-well-known English Catholics), Davenant not only makes his case from Scripture but draws on the entire corpus of church history as a witness that the Reformed Christian view of the Bible is the one most in accord with every major thinker from the early church through the Reformation. In addition to church fathers such as Tertullian, Jerome, and Augustine, Scholastic writers like Aquinas and Peter Lombard form a major part of his supporting arguments. Though I didn't count them, I'm willing to bet that there are more quotations and defenses drawn from Aquinas than there are from the entire generation of Reformers (Luther through Calvin) put together. Through the exposition of the book of Colossians, it is Davenant's goal to show that the Reformation was just that- a reform of the church not into something new, but into what it had always been.
3) The exposition of the text itself is clear and thoughtful, with a good mix of explanation and application.
4) This particular volume is especially handy, as it contain an index for each of the major themes of the book (subject, Scripture, and, especially interesting, an "Index of Questions Incidentally and Briefly Determined in the Work," which includes questions like "Whether the Pope of Rome hath apostolical dignity and authority" and "Whether it is possible for the regenerate man always to retain the habitual intention of pleasing God." Even more useful, the translator has included a series of notes intended to introduce the various theologians cites by Davenant. These notes are thorough and fair, giving biographical information about the theologian, a brief overview of his historical importance, and places where you can go to find out more (though of course most of the books referenced are now out of print- which means they're usually available as Googlebooks...). So, for example, if you don't know who "Cajetan" is, the note on pg 12 will tells you
Cajetan; otherwise Thomas de Vio, of Gaeta, another eminent defender of the Papacy, who flourished prior to Bellarmin [who forms the preceding note]... He wrote notes on Aristotle and Aquinas, and an Exposition on almost all the Books of the Old and New Testament... Though an amiable man, he entertained such lofty ideas of papal authority, that in his efforts to reclaim Luther, he became a strenuous opposer of that Reformer... He was made a Cardinal, and afterwards Archbishop of Pelermo...
5) And most importantly, Davenant's commentary deepens one's appreciations for Paul's fairly difficult letter.
Obviously the big challenge of this book is going to be its length. Few people relish the thought of sitting down to a nearly-thousand page tome that covers less than four pages of the Bible. But I can promise you that it is worth it. I encourage anyone and everyone to pick up this book and resolve to spend a year reading through Colossians along with Davenant. It will be well worth the investment. To help you decide, here is a sampling of Davenant's (translated) prose. If you can understand and enjoy this, then the commentary is for you:
[On Colossians 2:13, "And you, being dead in your sins and the uncircumcision of your flesh, hath he quickened together with him..."] We shudder to touch the dead bodies of our friends: but God is not only ready to touch our dead souls, but to embrace them; and not only that, but would even restore them to life. This should inflame us with mutual love towards God. (pg 456)
[On Colossians 1:13, "Who hath delivered us from the power of darkness, and hath translated us into the kingdom of his dear Son"] God translates us then from that melancholy and gloomy kingdom, when he illuminates our hearts by pouring into them faith, when he changes and restores our will by imparting grace; for, being enlightened and sanctified, a man is by that very act translated from the power of darkness into the kingdom of his Son (pg 158)
[On Colossians 1:14, "In whom we have redemption through his blood, even the forgiveness of sins."] He [Paul] points at Christ's bloody death: not that the previous acts and sufferings of Christ did nothing to merit human salvation; but that by pouring out his blood, i.e. in death, there was a completion of satisfaction. Although, as Aquinas truly says, any one act of Christ was meritorious in our behalf, yet to make satisfaction for the guilt of human nature which was under the bond of death, it was necessary that Christ should sustain death. But we are redeemed by this blood, or by this death, of Christ, inasmuch as it expiated the wrath of God, inasmuch as it dissipated the power of the devil. (pg 167)