By diary style I meant confessional, cathartic, deeply personal - but what really compelled me to use the word diary is the impression that the book at many times seems to have been constructed from a diary. For some reason, I think of that as something Lowry may have recorded on a daily basis. Tristes Tropiques by Levi-Strauss comes to mind. Rough hewn - think about the way some of the final portions of the book are presented.
Visual poetry is a fair description.
Mind you that rough-hewn is not to me a inherently negative quality.