In Early Christian Thinkers: The Lives and Legacies of Twelve Key Figures edited by Paul Foster the chapter on Tertuallian is written by Everett Feruson.
Honestly, I don’t know if I like or dislike Tertullian. Like many of those featured in this book the biography depicts Tertullian as a pagan, raised by a family who provided him with a solid education, who used his gifts for the church (pp. 85-87). We know him through his writings, those on (1) apologetics; (2) heresy; and (3) morality and discipline (p. 87). As a thinker he is the same person who can utterly reject philosophy while being indebted to how philosophy shapes his very argument (come to think of it, I know a lot of evangelicals like this). Tertuallian’s semi-contradictory approach makes him very nuanced and complicated. As I said, I don’t know if I like or dislike him.
Tertuallian wrote on a wide variety of subjects: God, the Trinity, theophanies, the incarnation, two natures in Christ, ”Christ’s work as recapitulation,” the Spirit, two advents, soteriology, types of sin, the image of God, the church, clergy and laity, the spiritual gifts, the weekly assembly, the eucharist, the role (or lack thereof) of women in the assembly, marriage after the death of a spouse, idolatry, the nature of Scripture, the canon of Scripture, whether Christians should be in the military, the eschatological judgment, Christ’s return, the millennial Kingdom, eternal punishment, and resurrection (pp. 89-95).
It seems like he was the first systematic theologian!
Ferguson names his most important contributions as having to do with his “position on disciplinary matters,” his view of Christians in the military, his “evaluation of martyrdom,” and his work with those trying to “reconcile with the church” after committing sins after baptism (pp. 95-96). I most respect him for his stance on Christian participation in warfare (though this is somewhat nuanced) and I least like him because he is uber-pious (i.e. his “morality” reminds me of the Oneness Pentecostal sect from which I emerged).
There is no denying Tertuallian’s impact of the Latin West and the theology of the western church. He was a great mind, but I doubt I want to go to coffee with him if he were alive today (though it might be fun to invite him to a movie theater to watch him squirm).