I'm an old player of the series, have been here since the GBA days and have played most games released on the west (didn't play radiant dawn, fates and engage). 3H is my favorite game maybe ever for the replayability, I love trying stupid builds on my favorite units, and thus have cleared it some 6 or 7 times.
Like many here I see many flaws in FW, but I also see a game made with passion and many experimental things. I've cleared part 3 twice at this point, once with all 4 routes done and one with only Leda done. This second time, I've barely left Dagsion most of the game, just kept doing auto-activities one week at a time for money, materials and went for training. I only left when I needed specific materials to trade at Vandahl's and getting some loot I knew I wanted).
Part 3 is SO DAMN HARD if you have cleared only one route. Your units are underpowered, you don't have enough units for the big stages. You don't have enough materials to repair your weapons, nor enough money to buy things. The battles are amazing. I've struggled so hard to defeat some bosses, as I couldn't ko them in 1 turn and pretty much all of my units got 1hkoes by it. And while I'm not a fan of the "defend dagsion" sections in part 3, doing it with only 14-15 good units made me split my party in 5 groups of 5, with 2 or 3 good units and some serviceable ones I've found. It felt really cool!
If you're looking for a chalenge, this is a good one!