I recently completed Doug Kelly’s first volume of his Systematic Theology (other volumes have not been printed yet) and would like to offer a couple of words on why you need to have this (yes another) Systematic in your library.
1) Doug Kelly offers an erudite and exhaustive discussion of the Doctrine of God that spans the entire history of the Church. The wide variety and positive use of Church scholars, including Patristic, Eastern Orthodox, and Roman Catholic authors (while still maintaining and defending Confessional Reformed Doctrine) is unparalleled as far as I can tell.
2) Building off the above not near enough can be said about the plethora of both Ante and Post-Nicene Fathers quoted to support and critique the author’s thesis on any given topic. If anything this volume will serve as a deep mine for those seeking quotations by the Church Fathers on topics concerning the Doctrine of Scripture and the Trinity (including the hotly debated filioque).
3) In the style of Old Princeton Dr. Kelly does not seek to teach us anything “new” but only to confirm what it is we as a Church have confessed since the last Apostle laid down his pen. It was quite refreshing to see how united the Church is on the Trinity and how quite novel and heterodox recent teaching has been on the central Doctrine that makes us Christians and not another humanistic religion.