Pretty graphics and unique concept are great but it's overly easy and lacks creativity with use of gameplay mechanics.
The gimmick would have been fine if the game only lasted for 2 boss fights (especially since you thought the first one was the main boss which it's not) but the game is overly long as they drag the game out for over 20 hours of play time dealing with 4 main bosses total. I never completed the game as I was fully sick of it after the 9 Tailed Fox boss and made my way into the mountains. I playing the game, getting bored and stopped 3 separate times, trying my best to give the game all the chance in the world since I like it's premise, and each time I became annoyed and left.
At the end of the day all the game has going for itself is that it's pretty and the story is unique. Which is all anybody seems to care about these days even though the gameplay is tedious. Not that the story is "good", just that it's unique.
With the lack of creativity in it's puzzles it can also be said that the game is overly easy. I can only remember dieing once against that weirdo with the sword in the forest, which for me personally was a sudden jump in difficulty which was never really repeated.