Now that the game has been out a day and we kind of see how the meta and such is shaking out, this game has a very strong base but does despirately need a few key additions/features if it's going to take over the world:
1. Some kind of long-term grind goal. FFBE has TMRs, Granblue has fusing weapons, and so on. Something that we can grind with our energy that will make us stronger. At the moment, the only thing you can grind is experience points and to a lesser extent, SP. You can't grind feathers. If you could, this might work, but alas, it's a 'do this three times a day and collect your rewards once a week' kind of thing. More dripfeeding is required.
2. Daily quests. Even if this just rewards feathers, or experience shards/crystals, we need some sort of daily quest. This keeps people engaged and doing things.
3. Events. Actual events with stories, new characters, and so on. Maybe introduce a new item that gives SP and tie it to events. Exclusive characters. Don't have to be top tier, don't have to even be good, but new characters or even costumes to equip to our characters would be great.
Give us those three and you have a great, healthy game. I worry that without these this game will get stale. Maybe they have these in the works.