I'm someone who generally has one or two gacha games in my pocket, without any intention of sinking a tone of time into them past the first month of its release, so for me, FE Heroes fills that role perfectly. This game got me to delete Tales of Link, and for that, I'm thankful.
I obviously wish there was more content, stuff like the Grand Hero Battles in particular which ramped up the difficulty to much, much higher degree would be great. For Narcian, I had to use a pretty elaborate tactic to make it all work for me, since I lacked the types of heroes that would let me handle the map using the strategy most people seemed to online. I had to send someone up the side, use a dancer to get him to move out of range of other guys, then use a character with the "Draw Back" ability to pull the dancer out of range, too. Maps that actually force you to use all of the various movement abilities available to you would be really cool.
But really, I do enjoy the game a whole lot. I managed to get a team of very, very powerful heroes without spending a single dollar on the game, and spent about fifteen dollars on it the other day just for fun, not feeling any of the awful, soul-crushing pressure to spend money that gacha games normally put on me. And those fifteen dollars also got me two very powerful heroes. So either the rates in this game are generous compared to other gacha games (and they are) or I just got really lucky (I probably also did that.)
I wish there was a more extensive PVP aspect; the friends list system right now is basically useless, which sucks because I have two siblings that play as well and would love to have a more interactive experience with them. At the very least, they should let me pit myself against an AI version of their team, arena-style.
But yeah, it's absolutely serving its purpose for me. I check in on it 1-2 times a day, and on days when they actually add content, I spend a decent amount of time with it. I do, like, really need them to push out a significant content update that I can't complete in a day, but even if they don't, I'm getting a lout out of it as it is. It's nice "collecting" heroes from Fire Emblem, though Erika, Lyn, and Lucina, the three I want more than any other, have all eluded me. I do still have a handful of heroes I like, and the ones I don't have any particular affection for are still useful in-game. On top of that, the game seems designed in such a way that you don't even really need 5*s to do most of it. So even if you get unlucky and are sitting on a bunch of 4*, the game is still totally able to be enjoyed. And then you can even make them into 5* heroes, albeit at the cost of an excessive price that takes actual months to get. But in other gacha games, while they have "evolution" and stuff that's much easier to achieve than the "unlock potential" is in this game, if you don't roll something good in those games, no amount of evolution or upgrading is going to make them any more than serviceable. In this game, a 4* Marth can be turned into someone worth having on a high-level arena team.
Uh, if my excessive droning on about it hasn't made it clear, I enjoy the game quite a bit.