I'm actually surprised of the divisive this expansion turns to be, some things are fair, like the amount of reinforcements and the way they appear in some maps, that definitely can use some adjustment, but things like Nil being useless seems weird to me, after all, that's the idea, you have to protect him, and even so, there are plenty of ways of use him, personally I put him the Micaiah emblem and I used him as support, so the only time I lost for his dead was my fault. The map design in general is more forgiving than people seems to give credit to, I played in hard and granted, it is, but, for example, chapter 5, the one which most hate seems to being receiving isn't so bad, in this map, you have to take care of 2 units, your avatar and Nel, the first one starts being attacked by a mage cannoneer which isn't very precise, giving you more than enough time to reach and heal them, then appears a dragon, if you have Lyn's Astra, is dead and that issue is resolve, if not, it's a 50/50 hit that gives you 2-3 turns to heal if it always hit, virtually taking away only one unit for you to heal him, after all, reinforcements doesn't appear from behind, making that healer safe. Nel is even less problematic, she's is principally being attacked by one enemy and even without rings (And you have access to them), it's not like she can really be one shotted, and she has more than enough elixirs to live until someone reach her, as a matter of fact, she can even take the reinforcements in the room if you know how to move (I sure did), if anything, is the amount of summons Fogado do to the end of the map what is unfair, because you have very little time to respond and it's a lot. I actually think the big offender of the flaws in the map design is the final one, it has a very specific way of being played and if you don't follow that way, it punishes you extremely hard, this map actually was the only time I lost and had to reset in the entire Xenologe. I completed the rest of the maps in the first try, and I don't think I am specially good at the game.

I really enjoy this fixed challenges, makes easier to mess with different strategies, even if some quality of life improvements would be appreciated, like the possibility of change the inventory of the new units in the preparations or that the inventory doesn't reset between maps

Therefore, the gameplay is not as good as the main game,
but not as bad as some people seem to believe. As for the story, I find it more compelling and interesting than the main one, even if it needs the other to be appreciated, at least most people seem to agree on that.

The Fell Xenologue definitely has it's issues in terms of difficulty scaling and the baffling way it's set levels work (Characters being at a set level on a per map basis, but never getting downgraded in classes; meaning that on map 1 you'd have a level 15 myrmidon Lapis and a level 15 swordmaster Kagetsu, like c'mon lmao) so I would definitely recommend just playing it on Normal There's some fun ideas with it's maps, but the tools you're given really don't feel up to par in a lot of situations so playing through it on higher difficulties is really not worth the headache, unfortunately.
Luckily, it's difficulty scaling is seperate from the main game; you can blaze through it on Normal and still appreciate the regular playthrough in your difficulty of choice, so that's a relief.

That being said, I genuinely appreciate the story a lot and Nel, Nil and the Four Winds are some of my favorite characters in both this game and the series as a whole, so it's peak actually!

Madeline and Gregory are kinda average as units, though the latter is the uncontested king of the Olwen ring but Zelestia, Nel and Nil are all really good and fun to use, especially the twins considering they interact with Emblems like no other as Dragon units.

Haven't dabbled with the new classes much but Enchanter's gonna be really interesting - Weapon Surge opens up a lot of new tactics especially for goofy challenge runs where you stick to one class for the entire team, something I'm quite fond of myself. Definitely wanna try an all Arts run with it's +5 MT to an Arts weapon of choice mechanic, someday.

So yeah, the Xenologue working the way it does is a bit of a let-down, but it's story and all the supports the DLC characters get are fantastic and they definitely made replaying the game worthwhile.

Whether it's worth the price is up to you, but as someone who enjoyed the main game a lot - this was no exception despite it's flaws.

Really enjoyed the harder levels in this. Some of them were genuinely challenging, even when you don't have to worry about permadeath. Sadly, there just weren't quite as many chapters as I expected. So many games have $30 expansions that have waaaay more content. But this expansion just kinda came and went. Also the story is actually pretty well written. But a lot of it is just executed so poorly in comparison to the main game. There were no animated cutscenes, artwork instead of movement, and a ton of awkward reused animations. This kind of took me out of the story a bit, even though I did really appreciate it and the themes that come with it. Overall, this entire expansion is a solid addition to the main game at most.

Man, this was a let down.

The new units are...fine. It's nice to have a manakete again, I guess, but Nel isn't really anything special. And the other units aren't either. And the maps, on normal, are almost insultingly easy. I had issues in the main game with how basically every boss has multiple health bars (which wasn't particularly fun and was clearly trying to compensate for how utterly broken engage attacks could be), but this time around, most bosses don't, making them hilariously underwhelming fights. A lot of the maps also suffer from just not being all that fun to play -- you're forced to deploy Alear, Nil, and Nel, sometimes with as few as two other units, and as mentioned, Nel (and Nil, for that matter) aren't great. Combine this with the DLC setting your characters' classes, levels, and inventory for you (which is a fun idea in theory, but obnoxious in practice) and you're left with levels that just aren't interesting. To top it off, the last level is gimmicky and dumb, in a game that had mostly avoided gimmicky dumb levels.

The story, at least, is enjoyable. It's not great, but it's at least a little better than the main game's story, so that's something.