Being, as most of you know, generally averse to all things Catholic, this is admittedly a stretch. Who knows, maybe it will help me avoid pulling a spiritual muscle later.
Francis was the Pantheist of the pantheists and the Ascetic of the ascetics. While it seems evident that he was altogether too mystical on these points, we must be careful to discern and not react. I am starting to feel that both pantheism and asceticism are somewhat undervalued in the western church, as we are usually not sensitive enough to beauty and rather too sensitive to pain.
Nature was created to be good, and, while it has felt the stinging curse of sin, it is still something good that has been marred and not something that is inherently bad. Christianity demands a deep apprecation for creation, not necessarily to see created things as God, but to see God in (through) created things.
Then there is the issue of the body. While certainly containing many weaknesses and often requiring restraint, the body, after all, is made in the image of God. Instinctively, we possess a natural, healthy concern for our flesh, (Ephesians 5:29) which the more extreme forms of asceticism attempt to reduce. It is nice to know that to be comfortable is not always evil, but we are reminded also of the uncomfortable side of things by injunctions to "mortify the flesh" and the account of Paul's urgent practice of subjecting his body in 1 Corinthians 9:27. Still, in all this, it must be seen that the solution is primarily a spiritual one, as in Romans 8:13. (Also Colossians 2:20-24, thanks Joseph for this one.) The virtue in restraining appetite is not to glorify abstinence, as the ideal in abandoning riches is not to love rags; rather, the aim in both disciplines is to love and glorify God, as in Romans 14:6.
Catholic literature is not much better than Catholicism in general, but perhaps it's analogous to eating something you don't like: it doesn't taste very good, but it doesn't necessarily do any harm either. So, with generous disclaimers, St. Francis.
St. Francis of Assisi, G. K. Chesterton
This book is more about Francis as a historical phenomenon than Francis as a person, and it presents him more as a hero of humanity than a hero of the faith, which is probably wise. Anecdotes and narrative are somewhat sparse, while G.K. focuses you on the big picture. Arguing that a major purpose of the Dark Ages was to cleanse nature of the polluted associations given her by pagan mythology, he portrays Francis as pioneering a new appreciation for creation as the world was "waking up" from this long hibernation. Using this springboard, with characteristic wit and perception, he develops the character and ideology of Francis throughout the subsequent chapters.
"He had made a fool of himself. Any man who has been young, who has ridden horses or thought himself ready for a fight, who has fancied himself as a troubadour and accepted the conventions of comradeship, will appreciate the ponderous and crushing weight of that simple phrase." - Ch. 5, Le Jongleur de Dieu
The Life of St. Francis, Bonaventure
Written by the 11th-century monk Bonaventure in that sleepy, devout, Catholic style, this book is a simple overview of Francis's life. For some reason, substantial portions of it are printed in a sort of free verse, only adding to the dreamy atmosphere in which everyone appears as either a seraphic saint or a satanic sinner. Makes you want to yawn.
If you can get past the references to the "supreme pontificate," as well as the making of Francis into a sort of god, there are a few jewels lying here among the stones. But they are so few that I'm inclined to just pick them up myself and spare you the trouble.
"We should not stave off a visitation of heavenly light even a little because of the light which we have in common with flies." - Ch. 5
"What a man is in God's eyes, that he is and nothing more." - Ch. 6
"In beautiful things he saw Beauty itself, and through his vestiges imprinted on creation he followed his Beloved everywhere, making from all things a ladder by which he could climb up and embrace him who is utterly desirable." - Ch. 9
And, perhaps the best 15-word synopsis of Francis's life and place in history to be found: "Where the scholarship of the teacher stands outside, the affection of the lover entered within." - Ch. 11