The largest flaw I can see after completing Rokka is its completely convoluted attempt at a mystery. It gives you no chance to figure out "whodunnit" on your own and uses magic to explain how events came to pass. (even more annoying magic that you do not already know about)
The second complementary flaw is how while Rokka no Yuusha is primarily a action show it spends its whole time centered around its convoluted mystery.
Now I see these two major flaws and several minor ones however I can honestly say I don't care. I went into Rokka with no expectations and was entertained on every episode. I feel the best way to enjoy rokka is to not have any preconceptions and to not spend your time trying to figure out a impossible mystery.
