Where to start? It destroyed some of the cast! Akihiko is a shadow of the self he was in Persona 4 Arena, and nothing like how he was in P3. It really detracts from the fact that Shinjiro is actually around to interact as this version of Akihiko drags him off half the time without giving him too much time to shine.
The game's comedy consists very little on its own merits. The P3 cast tends to actually interact and make jokes, but the P4 cast is almost 100% composed of references and inside jokes, even ones that make no sense. Teddie, Junpei, and Yosuke take up most of the game and form most of the comedy. They overuse every joke they can, from deadpan Yukiko to all the Rei food jokes.
The dungeons are great, I have nothing against them or their design.
THE COMBAT IS TRASH. They attempted to blend persona and Etrian gameplay. The persona elements? mostly left to RNG. Downs? Random. All out attacks? Random. One-Mores? Gone. Replaced with Boost mode which makes your next skill cost nothing. The more ppl with Boost mode the higher the chance of an all-out. But still, a bit portion of your strategy goes right out the window. Your goal changes from setting up downs and getting extra turns to hoping you get downs and abusing broken systems to get fights to end quickly. Stuff like Sleep and insta kills are somehow more broken here than in past Persona games. However, the persona system is interesting if not flawed.
Your party is compose of 5 characters split into 2 rows of up to 3. This is fine. Your characters have their base personas which get up to 4 skills that upgrade througout the game. You can equip sub-personas that give white HP and MP, which is only applied at the start of battles, giving you possibly infinite HP and MP. These also give you your extra skills. You can spend a ridiculous amount of effort to turn them into skill cards to permanently give your personas certain skills, but its set based on persona.
HOWEVER. On that end, you have to pay to get this done, AND have your persona above a certain level. Keep in mind that your personas level up separate the character and their main persona. AND THEY LEVEL UP AT A NOTICEABLY SLOWER RATE! The problem this creates is that you have to do a LOT OF GRINDING. In addition, you have to manage 16 characters and keep them up to level. It's not a requirement, but the game will badger you at certain moments if you aren't trying to keep everyone useful. This creates a problem with grinding to get not only money to get enough money to keep ppl equiped (the games gives you barely enough to keep one team setup), but also keep your party at a sound range and get your personas up to a level where you can sacrifice them to get skill cards.
Additionally, you may not want to sacrifice or even fuse up your personas! Guess what? YOU GET 16 SLOTS! THAT'S THE SAME NUMBER OF PARTY MEMBERS YOU GET! So you get no extra slots for use for fodder or for extras to get via dungeons. This creates a problem for late game where you have personas set aside for certain party setups, creating a space problem. There not even an option to store your personas anywhere like in 2. Couple this with a distinctly thin lineup of personas and you have an issue. The persona lineup you get and the fusion system are piss-poor.
There are not enough personas per level area to satisfy strategic needs or act as fusion fodder to fuse up persona strategies. Since you have to manage 16 chars and 16 slots, this creates a large conflict of who to sacrifice for what. I often found myself struggling for space and deciding to fuse away key personas because they were so underleveled. Add in that the system reverts to pre-SMT IV where only certain skills can be pulled up and its random and based on persona compatibility, and the system is punishingly limited. It's almost as if this was designed with you only having one character who switched personas in mind tbh. At least in the Devil Survivor games you get 24 slots, which is more than the party members you'll have in most situations and you can switch them out on the fly. Plus in that game you can fuse up the skills you want and buy demons in addition to fusing them. Here you have to rely on fusing them.
Lastly, it also retains the problems of the Etrian games. The menus are really backwards at times and don't effectively display all the info you need. They could be streamlined so much more than they are. It's not a huge ending issue, but its enough of one that its noticable coupled with all the other issues the game has here.
I will say the story is ok and some of the comedy is good. But for the most part the game just annoyed me and felt frustratingly designed. It tried way to hard to mash the two series togethor and failed utterly imo.