Excellent and readable history of Ante-Nicene Christianity. Schaff's main points (in addition to historical narrative and descriptions of the Ante-Nicene church fathers) are:
1) the practical nature of the early church. The church fathers were not generally great theologians (that had to wait until Augustine and the Reformers), but they were incredibly practical in their approach to the Christian life. The culmination of this was martyrdom.
2) the discontinuity between the early church and the later church, whether that means Catholic or Protestant. Basically, no one gets to claim these guys. We all have our origins there, but none of us do church or theology in exactly the way they do.
3) heresy, and the response to it. It's interesting how much of Christian doctrine comes out of people going off in crazy directions with their beliefs, and how hard the church fathers had to work to respond to the heretical movements.
4) the variety of orthodoxy. Within the body of believers, it is amazing how broad and diverse the fathers were. Basically, everything went, from Tertullian (a Latin-speaking lawyer who joined what was essentially the early version of the Pentecostals), to Origen (who was a Greek-speaking philosopher who approached Scripture allegorically), anything went within the bounds of orthodoxy.
There are way too many good quotes to put here, but I especially liked the conversion narratives:
-"O blindness... only a short time ago I was worshipping images just taken from the forge, gods shaped upon the anvil and by the hammer... When I saw a stone made smooth and smeared with oil, I prayed to it and addressed it as if a living power dwelt in it, and implored blessings from the senselesss stock. And I offered grievious insult even to the gods, whom I took to be such, in that I considered them wood, stone, and bone, or fancied that they dwelt in the stuff of such things. Now that I have been lead by so great a teacher into the way of truth, I know what all that is, I think worthily of the Worthy, offer no insult to the Godhead, and give every one his due... Is Christ, then, not to be regarded as God? And is He who in other respects may be deemed the very greatest, not to be honored with divine worship, from whom, when the day comes, we expect greater gifts?" (Arnobius, 857)
-"While I languished in darkness and deep night, tossing upon the sea of a troubled world, ignorant of my destination, and far from truth and light, I thought it, according to my then habits, altogether a difficult and hard thing that a man could be born anew, and that, being quickened to new life by the bath of saving water, he might put off the past, and, while preserving the identity of the body, might transform the man in mind and heart... So soon as I drank the spirit from above and was transformed by a second birth into a new man, then the wavering mind become wonderfully firm; what had been closed opened; the dark became light; strength came for that which had seemed difficult; what I had thought impossible became practicable." (Cyprian, 844)