Dr. Bill Mounce (son of Dr. Robert Mounce, who wrote another Revelation commentary, also colleague of Dr. Beale at Gordon-Conwell Theological Seminary) once joked and said that "you know it's good when it's so thick."
I took a New Testament Interpretation class with Dr. Beale, and also have his Revelation class notes.
Indeed, this is a brilliantly written book, which is well-written and thoroughly done from an amillennial perspective. Although this camp is not particularly big within evangelicalism (the predominant view being premillennialism), this particular camp has some advantages of being supported by strong scholarship. Beale's book is one of the best in terms of applying interpretational methods.
Beale starts off with about 69 pages of background on symbolism of numbers and the symbolic nature of Revelation. His main premise is that the beginning of the book of Revelation (Rev. 1:1) begins with "he revelation of Jesus Christ, which God gave him to show to his servants what must soon take place; and he made it known by sending his angel to his servant John..." The word "made it known" (RSV) in greek is esemanen (aorist active indicative, 3rd singular for semaino ... which should be rendered "to be communicated in symbols"). Thus, Beale takes the view that the book of Revelation should be read primarily symbolically unless there is ample evidence that it should not be rendered symbolically. He would note some of those symbols include numbers, lampstands, sword, etc. Thus, because of the symbolic nature of the book, the "1000 years" of Rev. 20:4-6 is to be understood symbolically rather than a literal 1000 years, rendering his view as "amillennial".
Beale does a great job in scholarship in interacting with other views, namely the premillennial and postmillennial views (especially readings of Revelation 20:4-6 ... close to 100 pages here), and also with other theories of the horsemen (e.g., Beasly-Murray, etc.) He even interacts with other commentaries and papers written on Revelation, as well as incorporating other literature (e.g., Jewish apocryphal writings) to analyze the text. Excellent scholarship!
To utilize this commentary well, you will need some basic Greek training (as Beale does utilize the Greek New Testament a lot, including doing textual criticism analysis, sentence flow analysis), like at least a first-year biblical Greek course.
This is indeed the best amillennial commentary (and probably the best commentary) that I've seen of Revelation. The two that are typically suggested by scholars include Dr. Robert Mounce's and this one!