Some quick reflections after reading Justin Martyr’s (est 100AD-165AD) extant works:
Note: This article was written before the author’s conversion to Orthodoxy.
1. I was surprised that his doctrine seemed so much less developed then even Ignatius and Polycarp who wrote decades before, even though he was writing from Rome. The highest position in the Church hierarchy that he mentioned was simply “a presider” that presided over the Eucharist. It appears that Rome’s church’s were not that centralized at the time of him writing, perhaps because of persecution. Yet, you have Irenaeus writing 2 or 3 decades later and he has a list of Popes and views Rome as a pivotal source of the preservation of doctrine…
2. This is something quite surprising considering that Justin Martyr seemed to think that the only source of doctrine was from the Scripture. From his writing, he appeared much closer to what we jokingly call “solo scriptura” then the historic “sola scriptura” position. Perhaps he got a free pass from the ancient church because he was a “philosopher,” not that anything in his corpus really reads quite up to par with contermporary writers of his day. Certainly even Ignatius, Clement, and Theophilus of Antioch were much better systematic theologians than Justin Martyr.
3. Justin Martyr’s view of the Scripture appears much smaller than ours and that of later ECFs. It appears that all he considered to be the Scripture were the LXX translations of the Hebrew Old Testament, and the four Gospels. He never quotes any of the Epistles or Acts as Scripture. He makes one mention to Revelation, which appears to him not to be Scripture but a recording of Apostolic tradition. He never quotes the Deuterocanon besides one possible paraphrase of Wisdom of Solomon. What we can learn from this is that at least in Justin’s mind, there was doubt that the writing of the Apostles can actually be considered Scripture, a position that seems odd at such a late a date. Clement, Ignatius, and Polycarp quoted almost the entire New Testament as if it were Scripture decades before. Justin appears to avoid it.
4. Justin’s lack of quoting the Deuterocanon coinciding with his preference of the LXX shows that he understood that the Deuterocanon served as an appendix of sorts for the LXX. This helps answer the question how a few fathers rejected the Deuterocanon yet would at the same time approve of the LXX.
5. Justin ironically makes certain interpretations of the Old Testament that are only possible if he had read certain other books. For example, the idea that the red thread hanging from Rahab’s window represents Christ’s blood is not original to Justin. It is first exegeted by Clement. Further, Justin makes an argument the Leah and Rachel are allegories of the Christians and the Jews…a similar allegory that Paul makes in Galatians four but with Sarah and Hagar. It appears that Justin felt fine with borrowing ideas from such respected writers, but he quoted the Old Testament directly, because he did not believe that their authority was equal.
6. Justin appears to believe a faith alone Gospel, with the necessary repentance to go along with it. He wrote that even Jewish Christians “likely” can be saved, which appears that his view of salvation was more expansive than later writers like Cyprian who argued that “there is no salvation outside the Catholic Church.”
I hope these reflections are helpful to anyone planning to read Justin, or simply wish they knew more about him.
Orthodox Christian Theology 
One note on the comparison of Justin with other fathers: Most of the other ones you mentioned were bishops or at least priests, and so it’s possible that someone like Justin (who I believe was a layman) did not have the same theological education, and this may account for why other fathers have a more developed theology. He certainly had a philosophical background, but this may have affected which issues were most important for him to consider.
He had a church meet in his house, so it is not entirely clear who the presider over the Eucharist was, whether he brought one it for him and his disciples did it themselves. Obviously, one can read a presupposition into it and say, “Well, of course Justin did this…” but we just don’t know any of that to be true.
Being that he appears to have been converted decades before his death and had a high status in the Church, it really is strange that his theology was not rudimentary. It probably speaks of the diversity and eccentricities of Roman Christianity i.e. Christianity in Rome in the second century. Churches located in other locales had less of a diverse population, and probably had more of a traditional belief at the time. The only other city quite so cosmopolitan at the time is Alexandria, and we can see of the zanier things and writings that came from this church not long after Justin’s time as well.
God bless,
Craig