I'm loving the game, but since you asked about difficulty, I guess I'll bite. I play on normal difficulty, but despite that, the game sometimes feels a bit rough. Especially when I get to the Scorched Sands chapter, which felt like it would have been impossible to keep Ephraim alive without a high level flier, to clear the units above him. There is a dark mage that can crit Ephraim, Knoll, and Duessel. Without Vanessa to clear that out, I'm not sure how I could have finished the chapter, since that side of the map will be flooded with reinforcements, many of which are mages that Duessel can't tank, and the sand that prevents him from meeting up with the team, on top of the fact that Knoll and Ephraim are dead weight when you get them initially.
And later on, even on fixed mode, there are quite a few units that just aren't strong enough and become a liability on the field. Most of the mages besides Lute felt very lacking in power or speed. Lute felt like a completely mandatory unit to use. Some bosses are just too strong to engage with anyone, so chipping at them from 3 spaces was the only way to keep everyone alive. To some extent, I feel like picking all the wrong units could make the game downright impossible. That or I just suck.
And the lagdou ruins are pretty brutal, but I can appreciate the fact that this post game dungeon is supposed to be very challenging. I haven't spent much time in the ruins so I won't comment on it until I try it some more. But with the tower of valni, I noticed the enemy ignores my units if they cant damage them. Which makes clearing this place post game a real pain in the butt. Since the enemy refuses to touch higher level units.
This mod is really great overall though, just trying to be as constructive as possible. I look forward to any future updates, having a blast with this.