J.R.R. Tolkien didn't understand why anyone would want to know about the life of an author. He thought the facts of an author's life would tell you little about what was important in an author's work. Nonetheless, he and his close friends and family permitted Humphrey Carpenter numerous interviews and other assistance in writing Tolkien's biography. The result is consistent with Tolkien's gloss on biographies: it tells us little about the significance of Tolkien's writings. Now and again, a fragment of Tolkien's life appears to have echos in The Lord of the Rings or The Silmarillion, but mostly the biography is an interesting peak into a somewhat ordinary life of a British academic.
Clearly, Tolkien was an enormously talented linguist and philologist, but it was as much his foibles as his talents that made him the important figure that he became. His early academic successes secured him his position at Leeds and later Oxford, but he never generated a huge mass of academic writing that he might have been expected to publish. Instead, he directed his energy into teaching, marking papers, and writing the literary work that made him famous. Carpenter's biography of him leads one to think that his literary work was mostly a way of avoiding the work that he might have expected to do in his academic position, but undoubtedly in this case, the fruits of procrastination and diversion turned out to be much sweeter than what he otherwise would have produced.
We can be thankful that Tolkien's publisher, George Allen, applied what pressure he did to ensure that Tolkien completed The Lord of the Rings. Without such pressure, not only would we not have this masterpiece, but Tolkien's larger legendarium, the Silmarillion and other works may never have seen publication. The world would have known Tolkien for a quaint children's novel, The Hobbit, and for revolutionizing Beowulf studies with his lecture Beowulf: the Monsters and the Critics. Instead of numerous volumes of his manscripts being edited and published by his son Christopher Tolkien, Tolkien's genius probably would have languished on slowly decaying paper in a forgotten archive.
Carpenter's biography is alternately generous with Tolkien and unflatteringly frank. In many respects, Tolkien comes off as a likable though unambitious man. In other respects, he seems a bit self-absorbed. It isn't clear just how accurate any of this is, but in all, Carpenter presents a believably three dimensional personality. There is, though, little to recommend this biography, except to Tolkien's most committed admirers.