The Star Child system is pretty interesting at first. Quickly sours because of combat system and poor decision with unlockable classes (addressed below)
Horrible EXP Curve. Monsters in the second dungeon give ~99 EXP a battle. Monsters in the 5th dungeon only give ~200 EXP a battle, despite being much harder. There's a monster that you can find at the bottom of the second dungeon that gives 3000 EXP.
The Combat is very boring, mostly because of the above. You just want to skip every battle except for the mid-bosses, the final bosses, and the large EXP monster mentioned above.
No way to differentiate between monsters visually. This would be fine, especially since you are given a spell to show what monsters are in a mob. But the spell wears off every minute or so, so you have to re-apply it. It sounds whiny on paper, but it takes like 15 or so seconds and some of the dungeons have ~20 rooms, so it adds up quickly.
Every room in a dungeon has a loading zone. Every. Single. One. And load times are not short. To make it worse, the dungeons rooms are separated by halls which also have load times and which can sometimes be very long themselves. There's just so much that breaks the flow of the game. I refuse to believe that Persona 4 can have similarly detailed looking dungeons without having to load every tiny room and this game can't.
There is some classes that you have to unlock with an item. These items are stupidly low drop/steal rate and are deep in pointless optional dungeons. I tried for about 2 hours to get 1 item to make a class and didn't find one. And when you finally get one, it's only 1 use (can only make 1 child with it). The items are so hard to get, they sell a quest DLC that raises your chances for them.
Conclusion: If you're itching for an RPG with Persona like "S. Link" aspects, this will scratch that itch. Otherwise, this game isn't worth the large amount of time/pat