BGM is really phenomenal, 11/10 as some have said before.
Graphic wise it's nothing exceptional or to write home about, but it's cutesy and your main menu live2D is really well done.
I didn't have any expectations for the story of a gacha mobile game and I didn't get any surprises, it's as bad as I thought it would be.
Gacha by nature is extremely expensive, so there is that, F2P friendly or low-cost? kind of, they copied from priconne and you can farm some units and get materials from events and stuff so you don't need to gacha THAT much.
Gameplay? mixed bag and the reason I quit. At it's core concept it's somewhat simple with some delicate intrincate details, at it's execution it's an RNG festa. Many skills translate into 10% chance of activation of (x) and the AI for auto mode is extremely dumb and frustrating. Game is also very poorly balanced at this moment due to the lack of units and the rock paper scissor system, although I suppose it will get better latter.
As the game is just released there isn't much to do, more content will be added later so look forward to that. Personally all the RNG on top of the RNG in the RNG killed the game for me, specially since PVP is extremely rewarding and your biggest source of resources asides from whaling AND your results in PVP are going to be essentially random with some slight variations depending on your enemy. It's not like priconne where units have a pattern or anything, they literally use their skills in a order, but that order is decided by RNG on battle start, and as said before, many skills are of "10% chance of X happening" so it's always nice to see your enemy get their 10% chance of dealing 500% dmg trigger but not you.
If you're interested give it a try, music alone it's worth it :)