XIII-2 has the concept of "Blood Damage." Each time you're hit with blood damage, you lose a portion of your max HP. In the first FFXIII, if you had a healer in your party you could recover from damage without trouble. But in XIII-2, you can't recover from blood damage, so you have to defeat enemies quickly.

Toriyama says that the staff is currently making adjustments to areas that they feel may be too hard. However, the final version has an easy mode, and you can switch to it whenever you want.

XIII-2 gives you the ability to freely change your battle leader -- that is, the character you're directly controlling -- during battle. When your current leader dies, you'll be switched to another character (this is different from FFXIII, where if the leader died, the game ended).

In addition to taking direct control, you can also assign attack AI routines, selecting from "normal," "concentrated" an "scattered." This is part of the new "Paradigm Tune" system.