One thing I noticed right away was the seperation between running around the environment and fighting an enemy. It harkens back to older "Dungeon View/Battle View" Final Fantasy's.
FFXII was seemless. You ran up to an enemy and the fight would commence in real time. In FFXIII you seem to run up to an enemy, choose to fight it, then the screen fades and you fight in a new "battle view" (for lack of a better term). This surprised me. I didn't think Square Enix would go that direction anymore after the FFXI and FFXII battle systems.
The environment/location seem to be the exact location you started your fight (as opposed to the older FF's where you would always fight in "the cave background" or the "field background"). Also, the number of enemies in the "battle screen" doesn't correspond to the enemies you see running around. In the demo, the player runs up to one enemy but when the screen changes to the battle screen, there are two enemies. Just like older FF's.