Just finished the game on Hard - Blue Lions route. Final level was somewhat tricky to keep everyone alive, though once I took out the hordes of enemies the final boss was pretty easy to gang up on.
Overall, I loved the game though. Didn't quite break into my top 3 FE games (Path of Radiance, Blazing Blade, and Radiant Dawn), but the story was very good overall and it probably had the best character-writing in the series.
On the flip-side, and maybe its just that the game expects you to play all the routes, but I feel like a lot of key plot points were forgotten in Blue Lions.
Spoiler!
Dimitri and Edelgard's mother was brought up multiple times as the person behind the Duscur Massacre, and yet she was nowhere to be seen in the ending. Rhea was apparently okay, but we never see her either. The Death Knight seemed to have some connection to Mercedes, a key member in Blue Lions route, and yet nothing was really explained even if they choose to fight. And I don't even know what happened to the mysterious masked group that was supporting Edelgard...I guess they just returned to the shadows and never came back?
Still...despite all this, I'm looking forward to playing more. Will likely do Edelgard's route yet...looking forward to it!