It is a very good game, among my favorites if not my favorite on the 3DS.
There are very good maps, and strategy elements like pairing and support, that both affect gameplay and story.
The story is good, but I have seen better.
Gameplay, and collecting/completionist elements like maxing supports for all skits, marrying different combination of characters and getting different interactions with their kids, etc. is great.
One possible point against this game (compared to other FE) is that it is too easy, even in Hard / Classic mode. Lunatic mode is like Normal difficulty.
Also this one allows you to grind freely (most other FE doesn't), so you can grind enough to make the game boringly easy if you wanted.
I would say you better not grind too much, and use strategy in your battles, it is more fun.
Also, there is a LOT of great content available as DLCs, so be ready to buy extra content (if you wish so, it is good).
The game is worth every penny, to the point I bought it two times actually, once for 40USD at the American eShop, I played the game fully and then gave that 3DS as a gift to a friend, and then I kind of missed the game after some months and bought it again (physical copy) for my European 3DS XL.
I would suggest you anyway to get a used physical copy in Gamestop or something. I got my European copy at Gamestop for some €30 or so.