Feel free to expand on that a little. OR hmu and I can rant about how much I love this game for a few hours. I'm currently playing through it again for the fourth time for the monthly challenge lol.
So as a preface, the only Fire Emblem games I have played (so far) have been Awakening, Fates (all 3 routes), Echoes, and Three Houses (full Golden Deer route, and halfway through true Black Eagle route). There's quite a bit I both enjoyed and did not enjoy so far in all of these games. Also for the record, before playing three houses I had considered Fates to be my favourite in the series. I know it gets a lot of hate for it's garbage story, garbage writing and garbage characters - but mechanically it was Awakening 2.0. Awakening was a great introduction into the series for me, but had a lot of serious holes mechanically speaking such as pair-ups being broken (and heavily RNG), stat growths being inflated, and ambushes on lots of map. I felt like Fates fixed a lot of these: making pair-ups less strong and more predictable, reducing overall growth rates, and ambushes only being reinforcements. (I hope I am using the terms "ambush" and "reinforcements" correctly here for this series)
As I had mentioned earlier, the sheer amount of game time spent in the monastery and doing the more macro-oriented content of the game was significantly higher in Three Houses than it was in any of the previous games. As a comparison; Awakening (26 chapters long) and Fates (27 chapters per path) each took me about 40 hours on my first playthrough, and about 25-35 hours on consecutive/repeat playthroughs on the harder difficulties. Three Houses only has 20 chapters and took me a little over 80 hours to complete. This has both downsides and upsides as a consequence; the characters get seriously WAY more fleshed out and appear less one-dimensional/gimmicky compared to the characters in Fates/Awakening which is a breath of fresh air. The downside is that I have to play for roughly twice the amount of time, for 6-7 less maps of the main story (as I'm disregarding the side missions that are available in any and all of those games) which is mildly frustrating. For Awakening, the army management portions outside of maps was very minimal and did leave something to be desired, as all the player could do was tinker with equipment & abilities, storage, read support conversations and visit the shop for gear.
Fates I found was a great in between when it comes to this aspect of the game. On top of the basics you did in Awakening, you would have your own castle with shops that differed based on which path you took. Additionally you get a different type of food and precious stone for each run that would allow you to invest more into a certain stat (food) and forge higher tier weapons of a certain type (precious stones). Initially that may sound long/complicated, but it was a fairly simple system that changed the game up even if you were to run the same route. Most importantly - it did not take up much of the player's time in achieving this extra layer of army management. There is a downside of Fates system here, which is the awful character writing where they were (and quite fairly) criticized for probably being the worst in the franchise. That being said, I've enjoyed the FE series as a whole more for it's combat and game mechanics than I have for it's characters (that being said, I do love some characters from all the games).
For the class customization in each of the games: they're all at least
somewhat different. Fates and Awakening were very similar, with the main difference being that characters in Fates had the option to change classes to what their partners or A+ tier friends were at the cost of having less base variety in classes on a single character. As a reference: in Awakening each character came as a base class and could second seal into any of two other classes but were stuck with that. In Fates, characters came with their base class and could second seal into one other class in addition to partner seals (changing to the base class of their partner) or friendship seal (same as partner but with high tier friends). In Three Houses, all characters could become any (non-gender nor lord locked) class if I am remembering correctly. In the surface, Three Houses seems like the best bet (more choices = better) but that feels less fulfilling when the majority of the classes all just eventually promote into their same version but with a mount. Early game, most characters start the same (noble or commoner) and experience a good divergence in classes when they promote to intermediate... only to converge again at the end game and mostly all hop on a (sometimes winged) horse. That being said, I don't dislike this class system so much as I am just... undecided still?
To quickly go back to Fates quickly as I failed to mention something: but the two core routes (Nohr/Hoshido) have two different cultures, and as such they have different classes based on those cultures. As an example, Nohr (more european inspired) would have their typically sword fighting class be the Mercenary -> Hero or Bow Knight and Hosido (more asian inspired) would have their respective sword fighting class be Samurai -> Swordmaster or Master of Arms. Having these differences, with different abilities and stat growths also helped to make the different routes play differently. As a final quick aside, this led to my favourite promotion class tree in the entire series, being the Spear fighter/master which has not made a return in the series since.
It is still a great game, and may very well takeover Fates as my favourite in the series after I play some more times through, as these are just my more initial feelings as I am still exploring the game as a whole. :) Also super sorry it took me a couple days to replay, I wasn't entirely sure what to cover/say and wanted to sit and think about it after you had confirmed wanting me to explain myself. ^^;; If there is anything I missed that you wanted my thoughts on, feel free to ask me more! I also just want to clarify, as much harping on the games as I may have did, I loved all of them a lot, and none of any of their deficiencies tore me away from playing them multiple times through.