It is believed and generally accepted by most scholars that the first gospel that was written -- Mark -- was written by a disciple of Peter. It wouldn't have been first hand, but second is very close. It is thought that this gospel was written only a decade or so after Jesus's death. The target audience were Jews and so it written towards them.
Matthew was written shortly after, targeting Samaria and so was writen a little differently. It is believed that Matthew was an actual disciple.
Luke was written about 60AD or so by Luke, a close friend and disciple of Paul. Paul did not know Jesus, but he did confer many times with Peter in Jerusalem hashing out doctrine. Luke targets the Gentiles and so was written differently towards them.
The last Gospel written was John, supposedly by John, a very young and close disciple of Jesus. It was written around 90 or so, supposedly after the Temple destruction in 70AD. It was written in a sort of protest against organized church rituals which is why the breaking of bread in the Last Supper never takes place. That later was converted into the ritual of Communion which made some early Christians nervous I guess. It also shows a higher Christology, folks by then more fully believed Jesus was fully divine and had been so from birth.
All the different books had different targets and were written at different times in the devoloping churches. Not all these guys consulted with each other so what should be more remarkable is not how the books differ, but how they are similar. At any rate, Jesus died around 33AD or so, the last book was written around 90 or so, that's still pretty close, especially when you consider this was a culture that prided itself on memoriazation and its oral tradition.