Mainly because it feels like a step down from the first Ninja Storm, seeing as the game is only partially free roam compared to the Ninja Storm 1, and lack of Ultimate Jutsu cut scenes make the battles short and leaves you with not much of a chance to use strategy... However this is only in comparison to the first Ninja storm, which to me stood as standard. Breathtaking Boss battles, no more Hide and Seek(well, almost), huge amount of characters, colourful scenery and characters bring to life the action. I'm not sure if I can honestly say this all makes up for it, because that begs the thought "shouldn't the original have been the foundation which Ultimate Ninja Storm 2 should be built on?". But then again, thoughts like those pale away when in the awesome online battles.
In summary, there were things I feel shouldn't have been left out from the original game, however improvements are welcome to fill the gaps, until Naruto Ultimate Ninja Storm 3, where hopefully nothing else is left out.