I really enjoyed this one a lot, and IMO it's a huge level up design wise from your previous work. The start was tough, just as warned, but once you get a few buddies and the systems start opening up it's a ton of fun. I really liked the heart and soul mechanics: it's a cool way to let the player experiment with builds without having to feel pressured about investing skill points, and it also makes each new enemy you encounter exciting (I get to use those skills? I get to summon HIM?! was how I constantly felt playing it). I managed to beat the final boss with a party of level 9 and 10 characters by keeping him constantly debuffed while buffing my own party's speed and having an AOE heal available almost always. I never had to stop and grind, either, though I suppose it would've made things a bit easier overall, haha.
The lore was cool: I love these kinds of settings and the scientific approach the game takes to the in-game mechanics, and of course the motif of fate being inescapable, even if the player tries to take the most seemingly kind way out, things still go like that... I was a little bit moved. Great work on this game!