"Work on philosophy -- like work in architecture in many respects -- is really more work on oneself. On one's own conception. On how one sees things. (And what one expects of them.) (CV, 24)
What makes "Work on Oneself" so compelling to read, also limits its scope and constrains how much "space" is dedicated to the actual philosophical psychology that Kerr is supposedly focusing on. The book was published by The Institute for the Psychological Sciences, whose mission it is to "contribute to the renewal of the Christian Intellectual tradition and to the development of a psychology consistent with the teachings of the Catholic Church."
This is apparent in Kerr's focus on Wittgenstein's writings (and the writings of others about him) and his espoused ambivalence regarding Catholicism (and even religion generally.) Though this colours Kerr's treatment and interpretation - I think it serves it well and adds needed depth and texture in many places.
Kerr also includes meaningful and enlightening references to (and writings from) Wittgenstein's friend and former student Maurice O'Connor Drury, who became a psychiatrist, rather than a professional philosopher.
One example:
"It would be a tragedy if well-meaning commentators should make it appear that his [Wittgenstein's] writings were now easily assimilable into the very intellectual milieu they were largely a warning against." (1966)
and this:
"A mental illness may indeed utterly disable the patient for the daily commerce of social life, but the terrifying loneliness of such an experience may make him more aware of the mysteriousness of our present being."
Kerr spends much time and effort creating this mosaic of the man [Wittgenstein] through the writings of others - particularly his students. That leads to a feeling that this book isn't so much about Wittgenstein, as it is about others' thoughts of him. Though some reviewers seem put off by this indirect treatment of the material, I think it makes that same material more compelling regardless of whether you agree or disagree with the assertions.
In all, this is not a deeply original work - nor could it be, I think, due to the space to which it's limited. However, it is highly readable and adds to the enjoyment and understanding of other works. I place this with Edmond and Eidinow's "Wittgenstein's Poker" and Nedo's "Wittgenstein: There Where You Are Not," which elucidate eachother's texts and Wittgenstein's work itself.