I have read and enjoyed so much of what dear William has published including his 17 New Testament Commentaries. Romans is not his best work.
William is so excellent at so many things: Providing the Jewish context behind the New Testament, explaining the motivations behind the various Epistles, as well as providing a treasury of literature to enrich the lessons.
In Romans, Barclay's worldview collides with Paul. When William brings his Arminian/Universalist point of view to Romans 8:28-30 things break down. His explanation of this fascinating passage is self-contradictory. It would have been more useful if he had given his take on it and then highlighted that other theologians such as Augustine, Aquinas and Luther had a different interpretation. William does this so well in some of his other commentaries, but not here.
William has great value, but take Romans with a grain of salt.