In this chapter-by-chapter and verse-by-verse commentary on Isaiah, the author succeeds admirably in making the prophet Isaiah's meaning clear. The scholarly and informative general introduction (over 70 pages) to the Book of Isaiah alone is worth the purchase price. As Dr. Unger points out in his Introduction, the author's unusual knowledge of Hebrew makes his work especially useful to students of the original text. The layperson, however, can benefit also due to Dr. Alexander's ability to make himself clearly understood.
I give it a 4 star for its riches of information; however, I would not recommend this book if you're looking for a simple aid to understanding the book of Isaiah. In terms of level of difficulty, this commentary is an extraordinarily difficult one to grasp. I would go so far to say that it is probably the most difficult commentary I have encountered.
A couple of features which make it so difficult for the average reader are as follows: 1) The repeated use of original language words without translation or even transliteration. You can gather some information from context, but it makes it tough to read smoothly. 2) The constant use of parentheses to further illuminate an idea. When I say constant, I'm saying there are parentheses in close to half of the sentences. Again, this takes away significantly from the clarity of a natural reading. 3) Although this is by far the least significant road block to reading the book, the fact that it was written in the 1800s causes some difficulty in terms of clarity of expression to a reader in 2020. I probably wouldn't even mention this if it weren't for the other difficulties, but piled on top of everything else, it is a noticeable feature.
If you are either using this academically or in the preparation of a deep study or sermon, I would recommend its use. If you have exceptional patience and don't mind the above difficulties, then you will get one of the most reputable commentaries on the book of Isaiah. It's reputable for good reason - it's content is phenomenal; however, stylistically (even for commentaries, which are usually somewhat dry), it was not my cup of tea. I recognize that commentaries are not judged primarily in terms of style, so for that reason, I give it a 4 star as a resource; but if it were more digestible, I would have given it 5.
"One of the best statements of the Post-Mil position in the form of a commentary, two of the best, are Calvin’s Commentary on Isaiah, and especially Alexander’s Commentary on Isaiah. J.A. Alexander." ~ RJ Rushdoony