As a fan of the Fire Emblem series, at first I thought that I will play this game forever and will be my only mobage. But these are the reasons why I decided to stop playing:

1. It's a gacha game and it has LIMITED CHARACTERS. Ofc it's a gacha game. I don't mind if it's a gacha game. But personally I don't like limited character thing. I'm not rich, so I'm pretty sure I won't get all those limited characters. I have spent a quite large amount of money just to get those chars, and I won't do it again.
2. It's a gacha game and new characters will always added. This new characters have a better skill than some characters. And the old ones are stuck with skills that may not be a meta anymore. Ofc that's how it is, if not, the players won't spend money for the developer and publisher to earn profit.
3. I love Fire Emblem series. I haven't played all of it, but the game's perma death, support links, gameplay, and character's progression (leveling up, stats, promotion) in FE6, 7, 8, 11, 12, and 13 made me love the game. But the mobage version is repetitive and demands so much time spent on it to get the most of it. Well, I think that's how mobage nowadays. I couldn't commit to spent so many of my times to this game. Because it's repetitive, I soon get bored. If you get bored, you won't want to spent more time to play the game.

I'm writing as a fan of the Fire Emblem series, while freely admitting I haven't played many mobile games. The Fire Emblem part of this game feels great. All the heroes are colorfully drawn with unique voice acting for each one. Building teams and fighting battles requires strategy, but not so much that it would be a distraction if you were playing this game for just a few minutes at a time.

The "mobile game" part of this game though was ultimately unappealing to me. It hits many of the same sour notes I have experienced with other mobile games. There is pressure built in to the game to do certain things in a certain amount of time. There is also pressure to spend real money on micro-transactions. It is not blatantly a pay-to-win type of game where they dangle expensive power-ups in front of the players' noses. Instead they monetize the "gotta catch 'em all" mentality by making it virtually impossible to unlock all the heroes from all the Fire Emblem games without spending lots of real money. This can be especially painful if there are heroes from your favorite games you would like to add to your roster. All you can do is buy in-game currency and then use it to unlock 1-5 random heroes at a time. Each time you spend currency to unlock a hero there is also the possibility of getting multiple copies of the same hero which further waters down your chances of unlocking anyone worthwhile with your cash transactions. So good luck building your dream team in any practical sense.

If you are careful with the little bit of in-game currency they give you for free, and especially if you are a fan of the Fire Emblem series as a whole, this game is worth some time. The story writing though is not at the same level as the retail titles, the maps are a great deal smaller, and the whole thing just has that "mobile game" smell to it.