Core game mechanics are interesting. With relatively little genuine move variety you can make a solid appearance of choice in fights. Overall I think its a strong base for people who like traditional JRPG-style combat systems. It exceeds the majority of those games, though that is admittedly a low bar.
When it comes to pacing though, the game gets into traditional grind issues pretty fast. After you have already demonstrated to yourself you can win a fight every time, but it takes you a few minutes, the fights quickly become a chore instead of something interesting. Simply put, I contend there are too many fights that are not challenging enough, it never feels like I am trying to push my limits with what I can do, it instead feels like I can take an extra 30 seconds in a fight to ensure there is no attrition, and that is an easy choice to make.
Overall, this first demo was easy enough that without leveling beyond killing everything in a line, I was able to get through it at nearly full health the entire time with neither of my guys falling or being at serious risk of falling. Being pressed into interesting gameplay only really comes out when challenged, otherwise easy, safe, and boring patterns emerge as dominant.
Now, to be clear, I am an above average gamer. I was genuinely confused when players had trouble with the difficult on a game that I helped create, with difficulties I viewed as being able to play while asleep, but there were a lot more pitfalls in that game due to higher amounts of choice. I think you can get a higher level of difficulty tuning in this game, with its relatively obvious 'combo' system.
As for specific concerns.. I suppose I can make a short list:
Infinite Sustain in combat by leaving the last enemy alive is too easy, and too boring at the same time. This should be discouraged somehow, even if its the enemy running away if they are alone for a couple turns.
Buff values are too nebulous. I have no indication of their value or duration, making them feel bad.
Might play through again to give better advice, but its running a bit dry at the moment.