Anyhow, as those of you who've read my banner know, I wrote a M.A. thesis comparing Luther to John of Damascus and therefore I'm very familiar with his work De Fide Orthodoxa. De Fide Orthodoxa was used very widely in the west. Aquinas makes many references to it in the Summa and Luther knew it. Chemnitz quotes it a great deal in Loci Theologici and also in the Two Natures book.
What it seems like to me is that Lombard is trying to write a western version of John's work- though I would need more historical proof to prove this. The point of John's work is basically the same as that of Peter's. It's a text-book summarizing the theology of the Fathers on the various loci of theology. Also, the books are structured the same way. Book 1 is Trinity, Book 2 is creation, Book 3 is Incarnation, Book 4 is sacraments and last things. Now granted this is the structure of the Creed as well, but Peter probably had John in mind since he obvious read John's work in that he quotes him. He quotes him infrequently, but he does so nevertheless. In terms of percentage, according to the translator (and simply reading it, you would get this impression also), 90% of the quotations are from Augustine.
So, how do the Sentences compare with De Fide Orthodoxa? Well, I'm only through the first book at this point, (whereas I have of course read all of John) so I can't make a complete judgment.
I will say that John has a much more sophisticated Trinitarian theology than does Peter in some respects. For example, in terms of interpreting certain Trinitarian texts in the NT John has much more sophisticated intellectual tool box given to him by the Cappadocians. So, for example, John interprets Jesus' statement "I am in the Father and the Father is in me" to be a statement about Perichoresis. For those unfamiliar, this is the idea that each person of the Trinity dwells in the other, that is, inner penetrates the other. Peter, following Augustine (who as I recall from my reading of De Trinitate about 7 years ago!) does not have the idea, interprets the statement as simply an affirmation of the unity of divine substance, which, if taken in the wrong way, could lead back to Modalism- which was of course always the biggest heresy in the west. Of course, it's not a bad way of interpreting it and if you're not a Modalist, then you can probably get away with understanding that way. But it's definitely not as good as the Cappadocian/Damascene explanation.
Another interesting piece is how the statement "the Father is greater than me" is interpreted. Following Augustine again, Peter interprets the statement to be a reference to the human nature of Christ. This is fairly typical of western Christology, which, following Leo the Great, tries to divide the two natures. Again, as a Lutheran, who follows Cyril, John has a much better answer, namely, that the Father is greater than the Logos in the sense of origin. That is, he has priority insofar as he is the fount of divinity. His person is of course not greater than the person of the Son. This again follows the interpretation of the Cappadocians, and, I think, is better because it avoids dividing the person of Christ.
In order to be fair to both of them, I will periodically report on how Peter continues to do. So far, I think the Damascene has won this round.