This is my favorite Fire Emblem game that I have played thus far.
The story was great--relatively light-hearted at first, and then grew even more intense and dark.
The voice acting was top notch, the voice actors did a really great job. Namely, Ian Sinclair. My god, did he do fantastic voicing Berkut. Especially as he's slowly driven to insanity through his own pride, casting away everyone he's ever loved for the power to defeat Alm. And then his death afterwards, realizing his mistakes and the error of his ways, and setting out into the skies above with his beloved Rinea... Absolutely broke my heart. Berkut is a great character on his own, but Sinclair took it to a whole new level.
The characters are well-written too, for the most part. They all get at least some involvement in the story. There are of course the main cast like Alm, Celica, Saber, Tobin, Clive, etc., but the rest of the cast doesn't feel too lacking in terms of character. They're all very unique.
The music is absolutely fantastic. Twilight of the Gods is a brilliant and hype final map track, and In a Silver Garden With You brings me to tears every time. Other great tracks include Scion of Purgatory, Pride and Arrogance, The Saint and the Sacrifice, March to Deliverance, and The Voice That Calls You.
All in all, the only things I'd complain about is the map design and lack of replayability.
The map design is true to the original Gaiden--perhaps a bit too faithful. Most maps, specifically Alm's route, are empty fields with one group of enemies in one spot, and then a few in some random corner of the map. Or it'll have most of your units in one area, and a couple others somewhere far, far away. It's kinda wack, honestly. I didn't mind Celica's boat maps, but I wasn't a fan of the swamp maps being right after the desert maps (which both impact movement negatively). That's just personal preference though.
There is incentive to play multiple times, with 2 difficulties, the free dlc pitchforks (which reclass anyone into a villager besides Alm and Celica), and a few in-game achievements that probably require another playthrough, such as Blitzkrieg (completing the game below a certain amount of turns). Otherwise, aside from self-imposed challenges like the ironman challenge, there isn't really all that much different each playthrough. Other games like Fates, Awakening, and Three Houses do this better, I feel.
All in all, very solid game. I feel not too many people have played it compared to the other 3ds titles, but I highly recommend giving this one a try, especially if you've played Three Houses as well, as they're somewhat similar mechanically. This game has a special place in my heart.