In the beginning, King of Thorn was excellent. The animation is fantastic (even the occasional lapses into animating the characters in CG are forgivable), I really enjoyed how the premise was explained (widespread panic caused by the 'Medusa' virus with a 100% fatality rate), and where it looked like the story was headed (post-apocalyptic survival/horror). However, somewhere along the line it fell apart.
At one point during the movie I thought to myself "That was much better than I expected, I wonder how they're going to tie this up" (i.e.- I thought it must be almost done), and then noticed that the movie was just shy of being merely 3/5ths of the way through. At about this point is where things started devolving. King of Thorn throws plot twist after plot twist, each more ridiculous/stupid than the last until the film's original purpose and storyline is all but forgotten. It struck me as a very soulless work- like something a computer could have made. Everything is cold, calculated, and very genre. The only thing that will ellicit any emotional response is the gore (either shock or, in my case, squeals of delight). Having said this, the characters are pretty adequately fleshed out for the format (film characters are generally subpar to their series counterparts who have far more time to develop naturally), despite the movie's own admission that they are stereotypes.
King of Thorn would have been worthwhile for me, were it to stick to the survival/horror genre instead of venturing into hokey and poorly-realized sci-fi. The ridiculous Sleeping Beauty references didn't help things either (I'm a big fan of fairy tales so I was less than impressed by their being used for nonsense).