This is a very controversial question. There are many opinions when it comes to Paul. However, I will give a standard answer.
First, Paul is seen by most scholars to be the most important person in the establishment of Christianity. This is not so surprising, because he wrote many books in the New Testament. Moreover, it was his missionary travels that brought the Christian message to Gentile lands. Indeed, he saw himself as the apostle to the Gentiles. From this perspective, we can say that Paul was foundational in forming Christianity as we know it today.
Second, based on the first point, he diverged from Judaism. He did this is two ways. First, he opened up the message of the Messiah to Gentiles in an unknown way. Second, he offered a theology that took away many of the Jewish practices. For example, he took away dietary laws, Torah keeping for salvation, and sacrifices in the temple. Jesus was the fulfillment of all of these things, according to Paul. Salvation was by faith and grace alone. This obviously angered many Jews. From this perspective, many Jews saw him as preaching a new message.
Third, did Paul's message differ with other Christians? This is a very hard question to answer. As was suggested in the first point, Paul was foundational to Christianity. With that stated, some disagreed with Paul, but Paul's interpretations won out. Some say that the dissenting voices were heretics. Others say that it was all based on power. In the end, people have to come to their own conclusions.