Martin Hegel is one of the most famous of biblical scholars, and the "Johannine Question" sums up his findings on the gospel of John.
Some of the more interesting points he makes: The title 'euangelion kata ioannen...was not given at a later date" (P 74) to the gospel. On the contrary. "Its early origin follows from a lack of any variant titles...these facts make a later transference very improbable...Not only the letter and the Apocalypse, but also the gospel, were connected with John of Ephesus from the beginning" (P 74).
He gives an explantion of how the gospel was spead, and, unlike many other scholars today, he argues for a "lively exchange between the leading communities...when the four earliest gospels were circulated" (P 75).
I was especially struck by the numerous historical details Hengel found. And by the fact that the gospel is written in a koine Greek with a marked semitic, even Hebraic flavor, a feature "which is also typical of the Apolcalypse" (P 110). There are huge similarities between the Greek John uses and the Qumran documents, as well as the newly edited Samaritan sources like Memar Marqua.
A pity this isn't more widely available.