Although Fr. Brown brings out the points of the Gospel of John with clarity, I can see where many more orthodox Catholics have trouble with his writings.
Historically, the Apostle John was author of the Gospel and referred himself as the "Beloved Disciple". Fr. Brown seems to want to hammer home that he only does not believe this, but the author of the Gospel, the Apostle John, and the "Beloved Disciple" are actually three distinct persons.
If you can get past the personal bias, this book can help in your spiritual development.