Ear Worm: Some of the electro music used in the fight scenes.
Narm: Both the Hiruko and Kimon clans hit it hard. Most of their shinobi are so decidedly bizarre and crazy that sometimes it's difficult to take them seriously.
Sequelitis: Although the series has its fans, it is widely considered as not up to the standards of the original movie, in a big part due to the deep changes in tone, setting and characters's personality, in another part due to Tough Act to Follow. Most of the fans prefer to consider it a separate continuity.
Special mention goes to the fact that we rarely see two or three ninjas from the same side together on screen, so we are deprived of the interesting interactions they could have.
What an Idiot: Dakatsu. Not only he offers Rengoku his sting tail in future exchange for the stone (what in the heaven would impede Rengoku from killing him with his own sting instead of carry out her part?), he later does exactly that and also idiotically demands her to perform a surgical procedure on him without knowing all of Rengoku's skills. The result is, predictably, Dakatsu being unceremoniusly killed.