The best modern King Arthur adaptation is a comic book, Once & Future, by Kieron Gillen, Dan Mora, and Tamra Bonvillain. The legends and myths of Camelot have an enduring appeal, and it's frankly no surprise to hear controversial director Zack Snyder - always fascinated by mythological archetypes - is particularly interested in creating a new King Arthur adaptation.
There's little solid information about this project to date, with Snyder settling for a single ambiguous comment. "I'm working on something but we'll see," he observed in one interview. "I've been thinking about some kind of retelling, like, [a] real sort of faithful retelling of that Arthurian mythological concept. We'll see. Maybe that will come at some point." This has led to intense debate about just what a faithful retelling of the legends of Camelot would look like - but, of course, it's actually not possible at all. The stories of Camelot are varied and contradictory, modified countless times in the various retellings, and there is no way to truly be "faithful" to them.
Given that is the case, the best modern King Arthur adaptation is actually the comic book series Once & Future by Kieron Gillen, Dan Mora, and Tamra Bonvillain. Where most Arthurian legends are set in the past, exploring the myths themselves, this story is set in the present day and explores the power of stories instead. In the creative world woven by Gillen and Mora, stories have a power all of their own, one that can be brought to life by faith. But in the modern-day, Britain has lost any real sense of its own national identity, with countless competing "stories" existing at once. Consequently, the version of King Arthur that is brought to life is a twisted and distorted nightmare, a being who barely understands who he is and who is open to manipulation by others.
The core concept is a fascinating one, with Once & Future confronting readers with all the different versions of Arthurian myth brought into play. The book even plays upon its modern political context, with current British Prime Minister Boris Johnson playing a background role as one of the antagonists; it's an amusing concept, given he has contributed significantly to Britain's current confusion over its self-identity, fancying himself as a historian who has written a strangely garbled account of the life of his hero Winston Churchill.
No doubt Zack Snyder would not consider this faithful to the subject matter, but ironically it is entirely faithful to the genre itself - to the fluid and ephemeral nature of mythology, and to the fact, every generation must learn to retell its own national stories for itself. Once & Future is easily one of the most fascinating Arthurian adaptations in quite some time, simply because it has a surprising degree of relevance.