The patch also incorporates Photo Mode, and the ability to hide the projectile weapons being carried on your back.
Here’s the full patch notes, provided by developer Team Ninja:
Additional Content
- New Game+
Added the ability to begin a new game on a difficulty level you have previously cleared with the weapons and Ninpo you obtained in your previous playthrough already unlocked. When starting a new game this way, your weapons and Ninpo will be reverted to level 1. - Photo Mode
Added Photo Mode to the in-game Options Menu. You can move the camera around within a set limit to take screenshots. - Ability to Hide Projectile Weapon
Added a «Show Projectile Weapon» option under «Game Settings» in the Options Menu, which allows you to hide your projectile weapon while it is carried on your back. 
Adjustments
- Lowered the HP of enemies in Ch. 8, «City of the Fallen Goddess»
 - Lowered the HP of enemies in Ch. 11, «Night in the City of Water»
 - Raised the number of enemies in Ch. 13, «The Temple of Sacrifice»
 - Raised the number of enemies in Ch. 14, «A Tempered Gravestone»
 - Raised the damage dealt by some of Ayane’s attacks.
 
Bug Fixes
- Fixed control issues that occurred when playing at over 120 FPS or while under high computing load.
 - Fixed an issue where controllers would not vibrate based on computing load or FPS settings.
 - Fixed bugs that caused the player to go out of bounds during certain chapters.
 - Fixed bugs that made it impossible to progress during certain chapters.
 - Fixed a bug which caused the game to crash during long play sessions.
 
Will you be giving Ninja Gaiden 2 Black another go now New Game+ has been added? Run through the classic campaign one more time in the comments section below.
[source teamninja-studio.com, via gematsu.com]