The Dimension Stride Linear Motion Battle System actually works out quite well on the NDS. It's got the feel of Abyss' Flex Range System, except with loads more air-time, which works out quite well. The battles, though a tad lacking in intensity, are fluid and easy enough to get into, without much problem.
Aside from that, the character designs and weaponry are quite hawt. There are quite a few firsts in the series, too, mainly the two gun-users (twin pistols and bayonet rifle). As far as the storyline goes, I've only started playing about a half-hour ago, so I literally know very little about it all. X3