OK, so I played the demo last night. Here's my impression:
I love the atmosphere of the Bresha Ruins, especially the rain drops on the screen, they were a nice touch. The background music is pretty catchy. I really like Mog, he's so cute!
(I actually thought it was a girl, cos it sounded like he had a young girl's voice, tbh).
The Mog Clock is a nice feature. It didn't take too long for me to get the hang of it. I also managed to capture at least five monsters. I varied between Cait Sith and the Zwerg Scandroid. I like the fact we're able to customize them. I had some trouble trying to heal at first, but apparently you have to use 'Wound Potions' that you get from Chocolina, then healing is more effective.
I spent a lot of time talking to NPCs, and did some of the sidequests. It's great that you're able to move and explore locations more freely than in the last game.
Atlas wasn't too much of a problem, tbh. I managed to weaken him using the device in the ruins, then took about five minutes to defeat him. If you've played XIII, then the battle system isn't really that much different in this game.
It took me about 2 hours to finish. I kind of wish it was longer, though.