You're not likely to go back to the campaign once you've unlocked all the characters (a fairly quick process if you avoid the tedious sidequests), and the introduction of online play is most welcome, even if it's rudimentary and in desperate need of a proper lobby. The game is at its best with a friend, perhaps someone turned off by the long-term learning required by more complex fighting games. Its longevity isn't assured, but the immediacy and fluidity of Ninja Tornado Fight makes for an entertaining diversion in-between this season's more time-consuming endeavors.
And hey, if you spend enough time with it, maybe you'll even learn what a Shippuden is. (Answers on a postcard, please.)