FFXVI PC demo seems to have some problems. Game still locks to 30fps during cutscenes (which is especially bad on a 144hz monitor). Graphics settings seem to not work? It makes the game look flat because I don't think AO is working for instance, and the textures don't look great either. The performance outside of cutscenes seems solid, but it does still hitch a little bit (though not in combat from what I've seen).
More a list of annoyances than anything, I'll still buy it. I think it's probably got some work to be done on it still though, so hopefully some of that will be ironed out by release.