Gree Animal Days was my all time favorite mobile game.
Be warned, before reading this review; the game was shut down several years ago.
There are lots of articles available online pointing to why the game failed. But largely, from what I read, the developers over promised and under estimated how difficult it would be to maintain their production schedules for new content and features which ultimately led to them shutting down the game as they could no longer maintain it.
There were not many games like Gree Animal Days at the time available in the android or IOS app stores.