Problems for me:
1) Fuck being so heavily multiplayer-centric for a mobile game.
2) I don't believe this combat system does well in screentouch media form. (Same problem I have with SAO:MD or Tales of the Rays before it closed, really)
3) Zero effort story.
4) Lots of random ass characters, little reason to use anything other than base 5*. So hope you pull them.
5) Equipment system is garbage.
Some problems are fixable. Some aren't. I loathe group formation elitism in MMOs enough as is, and you can actually fucking communicate in those. Mobile games, though, not so much. And I just don't feel like you should spend more time queuing than doing the fights you're trying to in a mobile game. Just gimme well-balanced solo content and don't have me competing against whales and we're generally good.