The Gospel of John is generally recognized distinctive from the Synoptic Gospels, amongst all possible perspectives of the reason, there is one reason very significant.
Just as a current historian can only write what was happening, a historian in a later time is able to provide insight of why it was happening. The Gospel of John was written 30-40 years after the Synoptic Gospels, by then John lived long enough to observe many of Jesus's prophecies became true, together with his spiritual mind, he was capable to connect things together.
While the Synoptic Gospels has 30% of events emphasizing on miracles and parables, the Gospel of John has only 10%, with 90% on Jesus's narrative and event description, more than 70% are focus in the last 6 months of Jesus's ministry, versus the Synoptic Gospels of around 40%. The number of events in the Gospel of John is not that many, just barely more than half recorded in Matthew and Luke, but it contains more details in the same event. For example, all four gospels had the witness of John the Baptist about Jesus, but the synoptic gospels only keep the key sentences (Matthew 3:11-12; Marks 1:7-8; Luke 3:16-18), whereas John provide full detail (John 1:19-28).
The gospel of John also contains a lot of John's own perspective and his retrospective narrative. So readers had to be careful not to confuse with the past and the "then" present. It is from his perspective, and his retrospective narrative, we have a deeper knowledge of Jesus, the son of God.
Who are the intended recipients of the fourth Gospel?
Though there is no internal evidence in Bible the condition of Christians in the late 1st century, but it is pretty clear that the external threats, such as the persecution by the Roman authorities, or the hostile Jews were never been a main concern, as it had never been a main theme in the letters of the New Testament. The major threat of Christianity came from the Christian circle, i.e. the false teaching from self-boosted apostles, false prophets and teachers, as well as the personal temptation from the current social atmosphere. We must know, this threat to the Gospel has been taking momentum 60 years after the crucifixion, it has became a strong current after 2000 years.
From the time the book was written until now, there is only one kind of intended recipient for the book, that is, those who can see and hear that Jesus is the Lord, who is the son of God and the origin of love, our faith and hope.
John marked his purpose in John 20:31
But these are written that you may believe[b] that Jesus is the Messiah, the Son of God, and that by believing you may have life in his name. (NIV)
*(b) an alternative translation to "believe", is "continue to believe", which is more accurate to describe "faith on Jesus never end".