Anyone hoping to write an exhaustive commentary on the Fourth Gospel will die long before they finish. The FG is widely recognized as being the kind of work in which the interpretational possibilities are almost endless. One can focus on Christology, election, sacramentalism, atonement and resurrection, the church, or none of the above. As a result, when one reads any commentary on John, the reader is advised to pay attention to what the author tends to pay attention to, because this will say something about the author's own theological emphases. This is good to know because not only will the reader get a better idea of where the author is coming from, he will also be on alert for ways in which the commentary may be imbalanced as a result of emphasizing certain things and neglecting others. Such is the reality of Johannine scholarship and the richness of the FG.
In the case of Carson, the reader will find the strongest evangelical defense of apostolic authorship among the commentary encyclopedia devoted to the FG. As a result, the reader will also find a commentary that takes the historical veracity of the narrative seriously and attempts to interact with the material from the perspective of considering the material to be normative and historically reliable. This alone separates this commentary from most other major commentaries on the FG in the last 40 years.
Carson properly interacts with the heavy hitters in Johannine scholarship such as Bultmann, Brown, Barrett, Smith, and Culpepper. Carson's interaction with Brown and Culpepper is especially good and provides a solid rebuttal to their differing approaches to literary interpretation.
The commentary is thorough in its coverage of the FG, but like all commentaries, is inevitably incomplete. Carson has his hot buttons just like everyone else, and the result is a good emphasis on issues such as authorship, testimony, election, and christology. The downside is that other emphases, like the much neglected motif of hospitality in the FG and its ramifications on christology, election, the church, etc is ignored. Is this enough to give the book a 4 star rating instead of 5? If so, then no commentary on John would be worthy of a 5 star rating for the reasons already mentioned. For what Carson attempts to do, he does it very well. For this reason, the book deserves 5 stars and should be the standard work on John that evangelicals in particular should consult.