In a recent response to Bart Ehrman, I addressed the common objection that the gospel of John is too different from the Synoptics for both to be historically accurate. In that post, I focused on how John and the Synoptics are more similar than critics often suggest and how John likely was intentionally supplementing the Synoptics by making his gospel largely different than the others, which offers a partial explanation for their differences. What I want to do at this point is recommend another resource that addresses the issue from another angle.
In the comments section of the thread here, I discuss some evidence that John was written late in the first century and that the fourth gospel probably postdates the Synoptics by decades, not just years. Given the evidence that the Synoptics were written about two or three decades earlier, that difference in dating offers a further explanation for why the Synoptics and John are as different as they are. It seems likely that the similarities among the Synoptics are due in part to their having been written around the same time. John was written decades later with an intention that it be largely different than the others.