It's a gacha game that plays like Final Fantasy Tactics.  Lots of characters to collect and it's really generous too when it comes to premium currency.  In essence, it is a really in depth gacha game that is f2p friendly, challenging, packed with events, and it actually has a good story.  

What sets it appart from other gacha games is that the characters you get arent just one trick ponies with 1 or 2 special abilities.  No, each character can have multiple classes with multiple abilities.  You have your warriors, tanks, assassins, long range, mages, healers, and support classes to mix and match to your liking and play style. Even a sh*tty 3 star character can be useful in this game.  Worth every star, mate.  Give it a go.