Xillia 2 is a hard sell. I personally really like it, but playing this game as a completionist will drive a person to drink, especially if they played the original. It recycles just about everything from that game - there are only a handful of new areas, none of which introduce anything astoundingly new. It's basically very much more of Xillia - more of its problems, less of its good qualities. It sacrifices the excellent sphere grid-esque leveling system in favor of an unintuitive, bland system where you gain skills automatically by picking between different elemental-themed skill trees. After the fun I had leveling in Xillia, this was maybe the most soul-crushing aspect of the game.
There are other huge problems too. The same sound effects I bitched about with Xillia are still here and being shouted every few seconds (mutton! Fresh mutton!). Someone from up on high must have issued a decree that the game be less dark, as several good storylines like Elize's are dropped in favor of light-hearted teenybopper RPG fare. It's a big step backwards in terms of a narrative, and few, if any, of the side stories match the predecessor's in terms of quality.
But truth be told, I'm still having tons of fun with Xillia 2. More of one of my favorite RPGs of recent memory isn't all a bad thing. The combat moves blisteringly fast and it's ridiculously easy to grind should you decide it's necessary. The two new characters are pretty awesome additions, and while I'm not fond of Milla's new voice actress, the rest of the voice acting is generally good-to-great.
Also worth noting is the absolutely fantastic translation work that's gone into this one. It sucks we see games take so long to come West, but when the result is this kind of smooth text and dialogue without all the jagged edges of, say, a Final Fantasy IV or a Last Remnant, then hell yeah, the delay is worth it.
So yeah, unless you're really a fan of the original like me, you might want to steer clear of this. But as it stands, I'm really, really enjoying the heck out of it.