In recent years much criticism* has been heaped upon Constantine Christianity as a distortion of Jesus and Christianity. Folks criticize this 1700 year old deal with the devil that allowed official, Roman recognition of Christianity at the expense of Christians (particularly the hierarchy) expounding the Gospel. In short, the critics argue that in the battle between truth and power, power won out. Eventually (over a 100 years) Christianity become the state religion, and thus lost its ability to speak, "truth to power." Since that time Christian Bishops and Popes and Patriarchs sacrificed the Gospel for the world.
Some of the criticism of this decisive moment in history is true and right. By willingly aligning itself to the official Roman order, the Christian hierarchy lost some of it's ability to fulfill the Gospel. However, too much of the frustration with Constantine Christianity is based on a poor understanding of history, culture, and Christianity.
First, what was the church suppose to do when Constantine the Great declared that Christianity was one of the state religions? Should they have said, "nah, we don't need that, please keep persecuting us"? Should they have said, "boy, we really need less people to believe and live the Gospel so that we won't be noticed by the Roman authorities and thus won't set Christianity down a path of destruction"? No, they did what any reasonable folks would do, they breathed a sigh of relief and thanked the Lord for their deliverance.
Second, was the devil in the deal or is there a little devil in all of us? Much of the justifiable criticism of Church leaders is because those leaders (popes, bishops, etc...) were venal, greedy, and corrupt, and used the church for their own ends. Plenty of church leaders throughout the middle ages and beyond acted with integrity, and used their power and money for good and justice. For example, Ambrose, a rich and powerful man, became Bishop (from deacon to bishop in a week), then sold his possessions, and more often than not advocated for the poor and the dispossessed. Meanwhile, he was an advisor to Emperors and part of the "inner circle."
The criticism of Constantine Christian System is more a criticism of human nature. I believe that State sponsored church ain't a good thing, nevertheless, we ought to be slow to criticize those decisions that saved people from persecution.
*I know I didn't link to any of the critics on the web, but that's because I'm lazy and tired. Just trust me that they are out there.