I finally got my go at the demo last night. Played through three times. Thoughts below:
1) It's not simple. It's not hold down one button to win. It's challenging and you are required to use your abilities. While you won't die in two hits, you'll be healing a lot more than you should early on. In a way the entire demo feels like one long raid boss. If you are inefficient in fighting early on, you will suffer during the actual boss fight. Very much feels like an action game from that standpoint. Think any Mega Man game. You want to try to avoid using energy tanks in a level where you don't know the boss just yet, because you want to have some leeway during the fight. If you suck at the level, you will not beat the boss. It's like that but with a bit more leeway offered.
2) My first two runs, I blew all my phoenix downs. I found that blocking is immensely helpful (sounds obvious but it isn't while you're playing), mostly because many attacks will hit multiple times (like the scorpion's missiles) and you can basically say, okay I can suffer 140 damage over three hits or 70 damage. Fail to do this a couple of times and you'll be using an extra potion.
3) My mother always used to tell me never to let my gas tank fall below half full in the winter, just in case you get stranded somewhere in the cold and need heat. The same can be said of potion usage. Always keep yourself up and heal after battle as much as you can without overhealing.
4) Speaking of potion usage, binding potions and cures to ATB is a brilliant change and instantly ramps up the difficulty. Coming from FFXV where healing items were both easy to get and terribly overpowered, this is welcome. You need your attacks to hit so you can heal yourself, but you have to choose, in the heat of battle, whether to heal or get off a spell or weapon ability. That choice can make the might easier or harder if you don't make the correct one.
5) This game does not play like any FF game you've ever played. Full stop. Almost every FF was 95% about party setup before battle. Now it's about what you can do when you're in battle because you have almost every tool available to you and it's still not easy. What is stunning about it is that the fighting in this demo has so much depth already, and you haven't even crossed the threshold of materia loadouts yet, or of weapon skills that become a factor in later portions of the game. Just based on what we see here, some skills are going to be more important for damage, some for staggering, and some for support.
All in all, this is a game I really just can't wait to sink my teeth into more.