I generally like G.K. Chesterton, but I had trouble making it through this. Chesterton calls the book an introduction to the saint, but there are only about 10 brief anecdotes sprinkled throughout his rants against modern views of saints, etc. As a biography, it is worthless. As commentary, it's probably a little better.
A short, sweet Life of Saint Francis of Assisi by a covert to Catholicism. Lots of St. Francis' life is left out, but you still get a good look at the Little Poor Man.