When I first heard of a Dynasty Warriors Fire Emblem crossover, I got extremely excited because we'd be getting a Fire Emblem game from a whole new perspective, Hack-and-Slash. While the fighting can seem repetitive (which seems more or less par for the course with these types of games), I can overlook it.
The story and original characters have their ups and downs. The story can seem a little lackluster at times and oddly feels rushed in some parts and dragged on for too long in others. Rowan and Lianna, while solid units, seem a little bland in terms of their character development. Darios on the other hand (spoilers ahead), was a wonderfully developed character. Even though I had a feeling he was one of the villains when I first saw him, it didn't make the big bad reveal any less spectacular.
As for the roster, don't get me wrong, it's pretty solid in terms of size and variety of units. My big problem with it is the representation. Out of the dozen or so universes that consist of the Fire Emblem franchise, only three, Shadow Dragon, Awakening, and Fates are prominently represented (five if you count Lyn from FE7 and Celica from FE Gaiden/Shadows of Valentia). There were so many characters that I would have loved to see appear in this game, such as Ike, Hector, Ephraim, etc.
Even though the story isn't the best, the History Mode provides a great alternative/post-story experience that can also help you in grinding EXP for your units, as well as gold and materials. The different scenarios present does provide interesting spins on tales from Fire Emblem's franchise history, using characters in-game to replace the original characters in said scenes (even if it doesn't make much sense).
Overall, Fire Emblem Warriors does have its flaws. With that being said, those flaws to me don't stop it from doing what it set out to do, bring an interesting new spin on a classic RPG franchise that I've come to love so much.