First off, the visuals are fairly bland, both in terms of the combat and the locations. The characters are faithful interpretations of how they've appeared thus far, and it's great to see them in a completely new way, but there's not nearly as much variety in the characters or locations as in Hyrule Warriors. Part of the problem is that there are too many sword users, something the developers acknowledged as being a challenge, but even the axe users' attacks look too similar.
For long-time fans the roster was extremely disappointing as it focuses on just two of the most recent games in the series (Fire Emblem Awakening and Fates) and the first game in the series (Shadow Dragon), but this is understandable, though, since those games are the most popular. On top of that, though, a huge part of the playable cast consists of the eight royal siblings from Fates, which seems a bit much. It's fantastic that the game includes support conversations, but since the cast as a whole almost entirely consists solely of royals, there's a loss of variety in terms of the characters' interactions.
Worse than the roster, though, is that many of the characters are clones. The developers gave characters different stat distributions to make up for this, but the differences don't affect the gameplay much. In two cases three characters all share the same moveset, which seems particularly pointless. There's a distinct feeling that the game was rushed as three characters are present in the game but not playable. I can't believe these characters are being released as paid DLC since they're already in the game, but my only hope there is that there will be more DLC beyond the three updates that have been announced so far.
After playing the game it makes a bit more sense that the game focused on the royals for the sake of the story mode, but the lack of variety in the characters is still disappointing. History mode is an improvement over Hyrule Warriors' adventure mode, but unlike Hyrule Warriors you can use whoever you want in most of the missions which makes things much less of a challenge. Also, there are far less unlockables: basically the unlockables are just the alternate skins for Corrin (male) and Robin (female), more powerful weapons, and one character with a unique moveset and two clones.
It's only because I'm such a Fire Emblem fanboy that Fire Emblem Warriors is as disappointing to me as it is. The Fire Emblem additions to the Warriors series, namely characters you can switch to on the fly and command, a "Pair Up" mechanic whereby characters can support another character to raise his/her stats, the rock-paper-scissors-like weapon triangle, and support conversations are generally worthwhile and enjoyable, and there's a good amount of Fire Emblem references for the fans. Maybe it's also partly Warriors fatigue setting in, but even though I worked my way through the story mode and a good chunk of history mode pretty quickly, I didn't feel that excited about it in general. I didn't have much motivation to finish all five of the adventure maps, and I'm skeptical that the DLC characters will be radically different from what's already in the game. I'm still holding out hope that additional DLC will be announced, but for now I merely appreciate that the game exists as hopefully it will expand the Fire Emblem audience even further. This wasn't the worst possible Fire Emblem Warriors I could imagine, but it's definitely not the best either.