by John Park
The early church fathers did not totally resemble the modern Evangelical Christian (EC) Theology nor Roman Catholicism (RC) completely. But who do they resemble more, or to put it another way, whose core doctrine reflects the early church more? And more importantly, who reflects Scripture most accurately?
Christ guaranteed Hades would not overcome the church. Though this does not safeguard against doctrinal error, it does guarantee somebody is right in regards to their core soteriology. In this aspect, it comes down to justification by faith alone or by faith plus works. Perhaps, saying differences in their "core soteriology" makes the issue cold and academic, but what really is on the line is the Gospel. As Paul said in Galatians 1:8 “But even if we, or an angel from heaven, should preach to you a gospel contrary to what we have preached to you, he is to be accursed [i.e. go to hell]!” Bottom line - We have different Gospels! And if we both can't be right, then one, as Paul said, is accursed.
EC gospel = Faith alone
RC gospel = Faith + (their church’s) Works
Here are some select quotes from the early church fathers:
Clement (80-140 A.D.): So all of them received honor and greatness, not through themselves or their own deeds or the right things they did, but through his will. And we, therefore, who by his will have been called in Jesus Christ, are not justified of ourselves or by our wisdom or insight of religious devotion or the holy deeds we have done from the heart, but by that faith by which almighty God has justified all men from the very beginning. To him be glory forever and ever. Amen. (Clement, Clement's First Letter, 32.3-4) 
Justin Martyr (100-65 A.D.): No longer by the blood of goats and of sheep, or by the ashes of a heifer . . . are sins purged, but by faith, through the blood of Christ and his death, who died on this very account. 
Augustine (354-430 A.D.): “Having now to the best of my ability, and as I think sufficiently, replied to the reasonings of this author, if I be asked what is my own opinion in this matter, I answer, after carefully pondering the question, that in the Gospels and Epistles, and the entire collection of books for our instruction called the New Testament, I see that fasting is enjoined. But I do not discover any rule definitely laid down by the Lord or by the apostles as to days on which we ought or ought not to fast. And by this I am persuaded that exemption from fasting on the seventh day is more suitable, not indeed to obtain, but to foreshadow, that eternal rest in which the true Sabbath is realized, and which is obtained only by faith, and by that righteousness whereby the daughter of the King is all glorious within.” NPNF1: Vol. 1, Letter 36, 25. 
Please see the references below for a more complete and thorough treatment of the issue.
Things to keep in mind: Many people believe that all the early church fathers were ROMAN Catholic. However, if you look at the literature it mostly states Catholic alone without the "Roman." What's the difference? It is much like how the word "gay" means happy, but in our cultural context, it has the meaning of homosexuality. The word "catholic" now has the connotation of being "Roman Catholic," but "catholic" simply means "universal." So when the early church fathers say they are catholic, they mean that they are part of the universal church, not the Roman Catholic church. Besides, the identification of being "Roman Catholic" came much later.
People also struggle with the idea that Roman Catholicism was the "only denomination or church" back then. This is simply not true. In fact, the Catholic church has many divisions and orders (i.e., Benedictine, Augustinian, Jesuit, etc.) and liberal and conservative arms. And even more telling is that the early church had several major centers: Rome, Constantinople, Alexandria, Jerusalem, and Antioch.
In summary, this is not a question about exactly resembling the early church. Even if we had 100% doctrinal identity, time, and place, culture itself would cause lots of differences. The real question is, does the gospel of the early church fathers match the evangelical or Roman Catholic gospel? Hands down the early church fathers believed in justification by faith alone.
References (with an abundance of direct quotes) for the Early Church and Justification by Faith Alone:
Other Notable Sites:
For great Church History Lectures (You Must First Go to the Church History Section):