I think I spent more time on this than I anticipated I would... Got all the way up to Chapter 8 in the Story, rerolled like a couple times for some unit I liked, was blessed with a 5* Abel that had a Brave Lance+. Absolutely killer. It destroys everything in its path.
Also got a 4* Clarine which has been very, very helpful, and as someone who appreciates the old characters a lot more, I'm having fun. Right now looking for some oldies in the Axe/Sword department to replace my current army squads, as I'm rocking a 4* Cherche and an awful 3* Palla for those spots. Cherche is good -- I'm just not too fond of the chara herself, but Palla is dreadful and I'm only using her for lack of anything better.
A Roy, Eliwood, Marth, Lyn or something along those lines would be perfect. I've got 16 Orbs RN and ran out of Stamina, so it'll have to wait til tomorrow. But here's hoping...
That said, the game's simple but quite fast and responsive, so it's easy to pick up and play for a bit. Tactically, I'd say a lot of the difficulty or lack thereof is related to how good your charas are, and at least so far the good 5*s have made a lot of missions much easier than I'm sure they'd have been otherwise. That said, map design-wise, it's about the same as you'd find in Awakening, which for a mobage is... acceptable, I guess? It didn't work for me as a full-fledged experience on the 3DS, but in this context I think they did a good job in making something addictive and that simply works.