During the Great Apostasy, Christ's Primitive Church or Christ's True Church was lost from the earth. What took its place was a distortion of the real deal.
Much of what was created in the Nicene Creed, the other Creeds, and the first Seven Ecumenical Councils was in direct violation of what Christ and the Apostles taught in the Bible. The Arians led by Arius knew this to be so, which is why they opposed the Nicene Creed.
http://en.wikipedia.org/wiki/First_seve ... l_Councils
Just like with everything else that has to do with religion, you will have to decide for yourself if what was voted upon in the Nicene Creed and the other Creeds was in harmony and unity with the True Church of Jesus Christ that Christ and the Apostles established, or not.
I personally believe that a Great Apostasy took place after Christ's Apostles were killed; but, you are going to have to decide for yourself whether you think this is true or not.