Saw it. I almost got up and walked out about a third of the way through, but I stuck it out.
Style-wise, the movie was all Guy Ritchie- very 'hip', with lots of CGI and slo-mo action. Pretty good effects, and the location shots in Wales were part of what kept my ass in the seat. A couple of interesting, vaguely Celtic musical pieces, too.
Story-wise, it was a gigantic snooze-fest. Change two names and take the words 'King Arthur' out of the title and you would have a stand-alone fantasy movie that wouldn't evoke a single hint of the classic Arthurian mythos.
I came away with the feeling that there was a pretty good fantasy-action movie hidden in there somewhere, maybe even a Jason Momoa Conan sequel set in ancient Hyboria, but this was NOT a good 'King Arthur' movie. Excalibur, made almost 40 years ago, is infinitely better in that regard.
Not entirely a stinker, but not worth full price in a theater, either. See it on 5 dollar day or wait for the stream.