Among the Gospels, John's is unique. That fact has long been recognized by Bible scholars and is really accentuated by the prologue to John. So how does this text in John relate to the Synoptics? To begin, the prologue itself has no real parallel in the Synoptics whatsoever. Matthew and Luke each preface their respective Gospels with an abbreviated genealogical record, while Mark basically jumps right into the story with the preaching of John the Baptist in fulfillment of OT prophecy. John, much to the contrary, leads into the story of John the Baptist with this profound theological commentary. John's prologue also introduces a number of terms and themes which contribute to an almost systematic theological treatment of the Gospel record. For John, history is incidental and theology (or Christology) is central - that is, history properly understood points us to the ultimate theological reality, Christ himself. Unlike the Synoptics, John seems to regard theological development as more important than the purely objective recording of historical events. (In fact, he might be inclined to argue that a purely objective record is impossible to obtain in the first place.) This is one reason Clement of Alexandria referred to John as a "spiritual gospel" (rather than an historical Gospel.)
Of course, John was in all likelihood aware of the Synoptic material already in existence, and arguably was under no compulsion to produce what would have become essentially a Fourth Synoptic Gospel. For failure to recognize his situation, John is too often misunderstood as a mystic, or even as a Gnostic. As we have seen, no one is more opposed to Gnosticism than John. So he's not one to be easily pigeonholed. On the other hand, John's theology is fully orthodox, and this is where his alliance with the Synoptics is indisputable (and his differences with them overstated). Where it counts the most, the Gospels are in complete agreement: Jesus is the center of attention: He is the Son of Man, preceded by John the Baptist, anointed by the Spirit, who teaches with authority and not as the scribes and Pharisees, who feeds the multitudes, who preaches the truth so as to open the eyes of the blind, who is delivered up by the Jews and crucified under the authority of Pontius Pilate, and who rises from the dead in victory. Indeed, John's prologue could be seen not only as a summary of his own Gospel, but as a basic statement of the gospel message of all four evangelists and attested by the entirety of Scripture: "For the law was given through Moses, but grace and truth came through Jesus Christ" (John 1:17).