Let me begin by making it clear that if you want to learn about Pauline Eschatology, this is NOT the book to read. . . . which doesn't mean that you shouldn't read it. Because it was published in 1930, it has several disadvantages. First, Vos writes in the old style - very long paragraphs and sentences. His chapters do not systematically address the issues; rather, they spiral into his view by a circuitous and often laborious route. Second, Vos is unable to interact with the recent developments in Pauline studies, especially with regard to the law, resurrection, etc. This is of course not Vos' fault, but it is something of which the reader should be aware.
This book is great if you are historically inclined and want to trace the development of inaugurated eschatology from its beginnings with Vos. But, don't stop here. Go ahead and read Ladd, Ridderbos, Cullmann, Dodd, Beasley-Murray, and Fee.
One last note: Vos' chapter on 'Chiliasm' is very unconvincing. He begins it by accusing pre-millenarians of psychological instability! Good for a laugh, anyway.
Vos's The Pauline Eschatology marks a monumental advance in Pauline theology. The fruits of over 40 years of vigorous Biblical scholarship, Pauline Eschatology is the last work we have from Vos's pen; and it is undoubtedly his most substantial contribution--his magnum opus. The most important developments that Vos makes are the connection between the Apostle's soteriology (doctrine of salvation) and his eschatology (doctrine of the last things). His chapters on the Resurrection and the Eternal State are brilliant. Based on penetrating exegesis, Vos insightfully works out Paul's Christological perspective of salvation, focussing on the objective acts of the Lord's death and resurrection as they inaugurate the new creation, the age to come, and relates that to the individual's personal salvation. Vos further delves the Apostle's pneumatology (doctrine of the Spirit) and demonstrates how the Spirit functions in his central message of salvation.
The appendix, "The Eschatology of the Psalter," is truly inspiring, opening up for his readers the Psalmist's God-centered piety and God-oriented hope.
Oriented toward the more scholarly audience, Pauline Eschatology is an invaluable resource for pastors and students alike, but is not completely beyond the grasp of the interested reader. If you pick up only one book on Paul, this one should stand at the top of your list.