This commentary is one of the most influential commentaries in Christian history. Much of Luther’s thought emerged out of his study of Romans and his reflections upon justification by faith. If you want to understand what Luther believed about salvation, this book is essential.
That’s not to say it is the most helpful commentary for understanding Romans. There are much more up-to-date and technical commentaries on Romans. There has been a lot of scholarship that has been done on Paul and his world since the time of Luther.
You don’t have to be a supporter of the New Perspective on Paul to understand that part of what Luther wrote was a product of his times. The first century conflict between the Jews and Gentiles is easily transposed to Luther’s conflict between the Roman Catholics and the Protestants.
Luther wasn’t only interested in what Paul thought, he was also interested in how to refute some of the teachings of the Roman Catholic Church.
That is not to say that this commentary is of no value. It is very helpful for understanding Luther’s theology and the religious conflict of his time. It is also of value for understanding Romans. Luther was a scholar and he did great work with the tools that were available to him.
I have read this commentary twice now and I expect to do it again.