This is my humble and fallible observation on 2 current prevailing manners of studying theology systematically:
All started when Agora Sg was looking for an introductory textbook for the group to learn about theology systematically. Here, i would avoid using the term 'systematic theology' because it is often being identify with one particular type of theological reflection that is organized in a fixed catechical format which is very well seen in the works of Louis Berkhof (1 volume Systematic Theology), Wayne Grudem (1 volume Systematic Theology), Millard Erickson (1 volume Christian Theology) and Norman Geisler (4 volumes Systematic Theology).
In this first manner of studies, one will usually list out the methods (prolegomena) then followed by the great doctrines (Bible, God, Christ, Man, Sin, Salvation, Church etc). And usually in each topics, we find certain prefix presumptions on a certain doctrine before a list of Bible passages to support that presumptuous doctrine. For eg. an author will first assumed that God is immutable with all kind of philosophical reasonings, and then he will back that claim with verses which either explicitly or implicitly support that presumption (Hebrews 13.8). Usually the author will discuss briefly each differing views on a certain issue before arguing for his own 'correct' view. And naturally, the author makes explicit his stand on issues. In other words, the author does have significant influence (possibly dictation) on a young reader (young in the sense of being 'green' or new to a particular subject). This is the first manner of doing theology.
On the other hand, there is a second way of reflecting on theological issues. We can distinguish the works by theologians like Alister McGrath (3 volumes A Scientific Theology, 1 volume Christian Theology, 1 volume The Christian Theology Reader) from the one mentioned above. This second method pays more attention to historical background, context and tradition, philosophical reasonings, and methods before going to the task of tackling doctrines. In this sense, the prolegomena is more detailed and comprehensive. This manner does help readers to be led into the flow of contemporary theological scene. When it comes to reflecting on doctrines, this second way will be more of conversant than one-way presentation. For eg. The author will explore many options on a certain doctrine and very often do not give a conclusive stand. The author prefers to allow the readers to explore more for themselves and, through that, reach a conclusion themselves. This way encourages readers to be adventurous and be accountable for their own theologies. The not-so-good impact of this second method is that readers do get frustrated struggling over unsettled issues which are raised in the book.
Objectively, i think, the second method is the one that would be prefer by theological institution for its educational integrity. This method might not provide conclusion to all issues, but isn't that the whole point of studying theology? It is a 'study'! Thus, learning should be encouraged and inspired rather than through dictation and indoctrination. Readers and students should be adventurous and explore as much as one can before drawing up one's own theological framework. Besides this method gives the student the accountability for constructing and preserving his own theology.
But to be fair, one must compare McGrath's introductory text (Christian Theology: An Introduction) with Grudem's (Systematic Theology: An Introduction To Biblical Doctrine). For McGrath magnum opus book on Christian Theology, his 3 volumes A Scientific Theology, is way different and more advanced in many areas.