I'll admit to being surprised by this. I've not played any of their games, but they're very well regarded, if not loved, by their fans.
No real details other than "We're going to make 360 games," so it could be that they're going to make cross-platform next-gen games, or they're going to release games on the 360 while waiting for the PS3 userbase to grow as the system goes down in price. Whatever Nippon Ichi Software does, though, its good news for 360 owners. Anything that adds depth and variety to library of a console is a good thing.