How is catholicism different to other religions of christians?

This is actually a very loaded question. There were other groups of Christianity that came before Catholicism, such as the Gnostics & the Nicolaitans. And, considering that there are so many distinct belief systems that seperated from early Christianity (including Catholicism) it makes it very difficult to make a really great essment. The disciples themselves had conflicting beliefs and they all looked upon Jesus Christ as the Lord and Savior. For each person on the face of the earth that knows of Jesus Christ, they have a different point of view. And, if each one of them started a religion, you'd have billions of Christian religions instead of thousands.