Consistency. Heavenly Sword struggles with it.
This is especially true for the first time you play as Kai, where enemies suddenly run at you and - reading the manual aside - you are not told beforehand which buttons on your control will provoke which result. It thus becomes a bit of a trial end error game.
The fact that it does change the gameplay is a great idea, but it is very sporadic and short lived when it does. As soon as you are getting into one type of gameplay element, you are thrust into a different one.
What it does do well though, is in it's story telling, graphics and voice acting. All of these are top of the class (or at least up there) considering this is a 3 year old game. Nariko's fighting controls are also very simple to understand and fun to execute. In fact I wouldn't mind those kind of modifiers in other games, although a block button in this game would not have gone unnoticed. :)
I recommend this game if you like a good story, but it can get frustrating at times.