I think it's great - it's a lot tougher than Lakshmi and Susano - which makes sense, since they were basically created to give people a way to get accessories/weapons and gear up. Shinryu, meanwhile, seems to have been created purely for the sake of a challenge.

My only complaint is the way in which the Minstrel's Ballad is implemented. Instead of being a fanciful retelling why can't it be touted as a loyal retelling of the difficulties that the Warrior of Light faced? They made story mode easier for obvious reasons but I feel like it cheapens boss battles by saying they're only that tough because a bard exaggerated things.