Just finished the demo myself.
It was pretty cool. I somehow was expecting better graphics, but oh well, they're fine. The battle system is really cool once I got into it. Even with the few starting abilities, I made up some good strategies depending on enemy positions and such. The paradigms and such are great, too, especially with the monsters adding a new layer of strategy. I completely destroyed Atlas with my buff-destroy-defend-destroy loop.
Crystarium is cool, too. It seems more linear than the Sphere Grid, but it's really not since you can actually choose which styles to upgrade instead of having to follow a line.
Upgrading monsters with items is interesting and a good idea, because if you have enough money you can just power level them. Nice that the demo gave you so many phoenix downs to sell for leveling materials.
Voices are decent. Noel is good, Serah is alright, the random characters like guards and stuff are actually pretty good too.
I dunno, the battles and the on-map movement were great, and the time/memory gate thing looks interesting. I might actually pick this up sometime.
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_foolmo_
'You are obviously intelligent and insightful' - Sir Chris about me