My new book on the Lords of Gower and King John needs a chapter on John, so I'm deep in research. Here's the first interesting thing I found:
[Talking about all the film depictions of Richard the Lionheart and King John] Since all these screen depictions showed Richard as the good guy and John as a creature of the night, I assumed that this was a stereotype that could quickly be dispatched after some serious historical research. Imagine, then, my surprise, when my own sleuthing in ancient documents turned up what is in effect a reinforcement of the stereotype. But the honest historian must perforce go where the evidence leads him.
(Introduction to Lionheart and Lackland by Frank McLynn)
I did find some good things about John:
He was well-read, was assiduous as a judge, personally supervised the work of the exchequer, oversaw the creation of a national customs system based upon standardised weights and measures, improved the 'pipe rolls' system of accounting and helped found the English Navy.
(The Movers & Shakers of Medieval England by Susannah Jowitt, p.15/16)
And some ideas in mitigation:
John's three older brothers, Henry, Geoffrey and Richard, had spent much time in childhood with both their parents, Henry II and Eleanor of Aquitaine, but for some reason John was packed off to Fontevraud Abbey at the age of three for five years, leading historians to suggest he was maladjusted. Recent speculation is that he was somewhat autistic, which would go some way to explaining his later bad behaviour.
Who thought King John would be so interesting!