The games biggest flaw is that the writing really falls off a cliff after you beat Kamoshida. Despite the games silliness he was a really compelling and convincing villain, a popular jackass abusing their power over you is especially common and relevant nowadays. And so is bystanders turning a blind eye because it's simply too much trouble to bother speaking up about it. Tigranes talks about expectations but I think the high writing expectations were set by the game itself.
The palaces and confidants were pretty hit and miss, but mostly hit. The biggest problem with confidants is that every confidant who features in the main story had most of their development relegated to the main story, because if their confidant events developed them too much then you could run the risk of their character being inconsistent with the main story (or having to try to account for their developments, which would be insanely complex in a game this large.) Some of the confidants had time gating instead, to ensure their confidant meetings could include good development along the main story, and I think these confidants were generally better.
Sojiro and Futaba and the family dynamic they have with the Joker is one of the highlights of the game imo, with Sojiro slowly come to trust and appreciate you, and Futaba opening up and overcome her trauma. I love the dynamic of three unrelated people forming a family together around the tenuous connections life has forced on them.
Takemi and Kawakami are blatant fetish bait on the outside, but I found both of them to have pretty interesting confidants. I think it's because they're actual adults so instead of "I'm an emotionally retarded teenager," they have really legitimate and difficult external problems to solve, although I seriously dislike how many confidants involve you changing hearts in mementos. It conflicts with a lot of the story beats that show up later in the game. Iwai was good for the same reasons as Takemi and Kawakami.
Ryuji and Ann and Mishima were pretty good because they got so much development in the Kamoshida arc but past the Kamoshida arc they got turned into parodies of themselves which I found disappointing. Their confidants felt like boring filler and the enjoyment I got out of hanging with them was mostly because I felt a bond with them from the first arc.
Haru and Makoto were probably the most boring characters in any video game ever made. They didn't get much attention in the main plot (Haru's had all of hers stolen by Morgana,) and their confidants were extraordinarily boring. Maybe you need to romance them to see what's special, dunno. Yusuke didn't get much development either but he eventually won me over through his sheer autism.
Morgana, Igor, and the Twins were all enjoyable and got development throughout the games main story. Other than the blunder arc where Morgana left the team, I liked all of them.
Maruki and Akechi were both great and extremely relevant characters. Maruki was very believable and I like the contrast between him and the protagonist, in that the protagonist is a strong and willful person accepting the truth whereas Maruki is weak and awakens a Persona specifically to help the world run away from it's problems. Akechi isn't really believable at all but I love the way his actor chews the scenery and makes him come off like a complete lunatic. Unfortunately the way the rest of the cast treats Akechi is pretty weird.
Ohya and the politician were the only confidants I didn't max so I don't have much to say about them. Hifumi was extremely boring so I don't have much to say about her either.
The game was... weird on Merciless. The biggest problem is that SP and HP management throughout a palace is extraordinarily generous, so the only way to challenge the player is by making fights very swingy. Every time I died after the first palace was me getting burst down in a single turn because I felt too lazy to buff. Vs enemies that could be effected by statuses or had weaknesses, it mostly came down to abusing weaknesses and elemental attacks. Against bosses the combat felt like an mmo, with one support and healer and two dps characters slowly draining a bosses hp. I mostly enjoyed the combat but about 2/3rds through it got stale and I started ignoring most enemies.
Kamoshida's arc was great since he was such a good villain and everything was fresh. A lot of people complained about the pacing but the game was intriguing enough that I didn't mind it, I'm sure I'd be frustrated at it on a second play through.
Madarame and Kaneshiro both had fun palaces but were boring villains. Madarames great crime was plagiarising art, which is a shitty thing to do but feels irrelevant next to the other villains. He also was said to be abusing his students, but the game never really goes into detail on that so all of the hate you have towards Madarame comes from his shadow's behaviour and the reveal that he let Yusuke's mom die. Kaneshiro was even more boring since he didn't have a personal connection to any of the characters, thankfully his palace made up for it with some amazing puzzles and fun design.
Futaba's arc starts off strong with the Medjed and Alibaba intrigue (although it was extremely predictable,) but the execution after that leaves something to be desired. It feels like they just threw a bunch of mental illness neet tropes together, and the changing of her heart doesn't get the weight it properly deserves in my opinion. It was still nice to see them try something different, and Futaba becomes a great character once you get to know her.
Okumura's arc finally gets back to the main story, but this was definitely the weakest section of the game. Morgana has his "I REFUSE TO TALK TO YOU," arc which is made worse by Ryuji acting like a shithead. Haru is introduced but she gets very little development since a lot of what's happening is focusing on Morgana. Around this time the game implements a gap between what the player sees and what the characters see. At the time it's the players seeing an obvious consequences the party isn't aware of (Okumura isn't the murderer, and instead will be murdered to frame you.) This kind of dramatic irony doesn't work well in an RPG where you're in direct control of the characters, because you're forcing the player to perform actions that they know are a terrible idea, unlike a book or a movie where the characters perform actions irregardless of the audience.
Sae's palace is a big step up, and we're finally getting close to the place we started the game at. The concept and design here is really unique, and the music and visuals of her palace are top fucking notch. Everything goes as planned until the big reveal. Here the game has another gap between the player and the characters, but this time the characters are forming a plan without the player knowing and it's revealed to you in the moment that it strikes. There are many moments before this scene where your screen gets all blurry and weird to indicate lost memories, and I genuinely thought that screen effect meant some powerful being was observing me and told the cops. So I actually thought the line about their being a traitor at the beginning of the game was a bait. This made Akechi's betrayal genuinely fucking surprising and got me totally lost in the moment, but it didn't feel cheap since everything was adequately foreshadowed many times, and the plan to keep Joker alive was pretty clever.
Then we enter the end game. You're pronounced dead and you now have the space to take down Shido. Shido isn't a particularly interesting or complex villain, but he was built up throughout the entire game and has encountered the protagonist many times so he was good enough. I really enjoyed the conspiracy angle that was going on, with Shido having killed Futaba's mom and utilising some top secret research, it's just like politicians in real life. His palace was a mixed bag, with some real annoying rat sections but I enjoyed getting the five passes and I loved the boss fight. Felt cool as hell 1v1ing Shido to finish him off.
The killing god arc was pretty strange. I think it was adequately foreshadowed, but at the same time nothing can possibly make the escalation from killing a politician to killing a god seem natural. The execution left a lot to be desired, the hamfisted "EVERYONE IS A PRISONER OF THEIR OWN MAKING," isn't bad, but I don't believe it was treated with the dignity and weight such a statement requires. I did enjoy seeing the classic Japanese obsession with gnosticism and jewish mysticism, and getting the gang out of The Velvet Room felt like an appropriate moment of re-awakening, wherein the will of the main cast is asserted for a second time in front of their greatest foe yet.
Then you get to the third semester. It honestly felt a little tacked on, but I think it was one of the strongest parts of the game (although it was too short.) Everyone wakes up in an alternate reality, but Joker and Akechi are the only ones who realise it of their own accord and have to work together to find out what's going on. This immediately makes Akechi and Joker's rivalry a lot more interesting to me, since it means they're really the only two "players," in this story. The Phantom Thieves who joined you in rebellion earlier are enraptured by this new reality and you need to shake them out of it for them to realise what's going on. Not only that but it's revealed that the only reason Maruki had the power to create this new reality was because of their wish for it. This really changed my perception of the Phantom Thieves, since they really are just followers who would never have gotten so far without you, although I supposed it makes the power fantasy aspect of the games stronger.
One of the weird aspects of this arc is the way it makes the Phantom Thieves seem like hypocrites. They spend the entire game changing the world by changing peoples hearts, making peoples lives better without those people having to actually do anything. Yet when Maruki does the same thing on a greater scale they criticise him and stand against him for it. In my eyes the early palaces you did were clearly justified in this lens, The Phantom Thieves were using their own power to rise against problems that threatened them (regardless of how much they talked about justice, it was always a personal matter.) And the point in the story where they "lost their way," and fucked up was the very point where they went after someone they had no connection to (Okumura.) Changing hearts in Mementos, on the other hand, is extremely similar to what Maruki is doing, and it killed my immersion that the game does not take notice of that.
You may have noticed I didn't mention Yoshizawa. That's because she was boring waifu-bait and her only purpose was to make the player mad when Maruki tentacle mindrapes her.