So far there's a fair handful of small issues with the game, although overall it's quite solid.
First, the aesthetic things; stuff that doesn't directly impact gameplay.
Some menus look a bit glassy and sci-fi, some menu items could be redone to fit FE's aesthetic better. In particular, sliders in the options menu and the sovereign creation screen.
In wide resolutions, on the title screen, all or part of the elements at top and bottom may be cut off.
In the tech menu, there are black lines that appear around the tech icons, especially when dragging.
In the cloth map, rivers are shown even when they're actually in the ocean. In the zoomed in view, rivers seem to have no beginning or end, and aren't really visible in forests.
The graphic for the Armorer's Forge is missing from the cloth map.
Now, some things that actually matter for gameplay.
the spell "Heal" is too weak. With no life shards, it's worth two or less attacks at the beginning of the game. With life shards it's better but it's still only rarely more advantageous to cast Heal than to just attack.
A quest, I don't now know the name, has a merchant sell you a treasure map, and sends you to a reasure location. That location has a dark cloak described as having to do with shadows. The cloak did not appear in inventory until significantly after, and seems to sporadically disappear and reappear.
Throwing daggers don't seem to work properly. Either that or I just can't figure out how to use them, in which case this is an interface issue.
The game doesn't scroll through use of the edges of the screen or through use of arrow keys. Zooming out and zooming in elsewhere works fine.
Costs to upgrade units are ludicrous. Even with experienced units and playing as Carrodus it's better to just hire new guys with full gear.
an army of drakes somehow got onto a tile occupied by my city. I can't attack them and they're not leaving. They can attack me, though. On a similar note, I got a stack stuck on an impassable mountain at one point. I could not move them off manually, however my attempt to do so left them with a move order which was resolved at the end of the turn.
On the plus side, the game is quite stable. It took something like four or five to crash, and I was even able to tab out to a text document to take these notes with no crashing (although I suspect that may have caused the scrolling issue).