Very happy that we have a new Theatrhythm on modern platforms, especially since All-Star Carnival was only in Japanese arcades. I logged it as mastered due to getting the platinum trophy on PlayStation, but I have not FC'd every song on Ultimate or even beat every song available on Supreme, so there's still more for me to work towards in the game. I only have one complaint, which is that the EMS charts can be disorienting, splitting the player's attention between the cinematic in the background and the notes falling from above. It may have also been my mind playing tricks with me, but it did frequently appear the the notes weren't falling as smoothly, meaning possibly that it runs on a lower or inconsistent framerate when playing on EMS charts. Those are only a small fraction of the tracks, however, and they are still enjoyable as is, so I let it pass. The tracklist is enormous, meeting close to 400 tracks in the base version and around 440 at launch if you invested in the Premium Digital Deluxe Edition, which will reach 500 tracks when the first three season passes are finished. The gameplay is very simple, but can still manage to be a challenging experience at it's highest difficulties, enticing both rhythm game veterans or people that just like Final Fantasy/Square Enix titles.
Despite the title simply being called Theatrhythm instead of being inserted with a series name like Final Fantasy or Dragon Quest, the title completely consists of Final Fantasy music if you opt to not purchase any of the DLC. The DLC may not cover all your bases either, even within the Final Fantasy series. As it stands, there are no Dragon Quest tracks currently announced to be in the game, nor does it seem like there will be. Kingdom Hearts: Melody of Memory was released recently, so it's doubtful that you'll see any songs from the series in the game. In addition, developer interviews have confirmed that there are currently no plans to add Final Fantasy XIV: Endwalker or Final Fantasy XVI tracks, so those are in the air, dependent on how long SE wants to support the game. That being said, it's still a new game with a lot of possibilities to be explored, especially if they intend on treating this game like All-Star Carnival and continue supporting it long term.
Overall, it's definitely worth the purchase. I think the game probably lends itself better to the Switch than it would for the PlayStation, considering the portability and the fact that you spend the majority of the gameplay looking at the right or bottom of the screen is likely preferable on a smaller screen. That being said, I can personally confirm that the PlayStation version works perfectly well, so either purchase should work out well for you.
Despite the title simply being called Theatrhythm instead of being inserted with a series name like Final Fantasy or Dragon Quest, the title completely consists of Final Fantasy music if you opt to not purchase any of the DLC. The DLC may not cover all your bases either, even within the Final Fantasy series. As it stands, there are no Dragon Quest tracks currently announced to be in the game, nor does it seem like there will be. Kingdom Hearts: Melody of Memory was released recently, so it's doubtful that you'll see any songs from the series in the game. In addition, developer interviews have confirmed that there are currently no plans to add Final Fantasy XIV: Endwalker or Final Fantasy XVI tracks, so those are in the air, dependent on how long SE wants to support the game. That being said, it's still a new game with a lot of possibilities to be explored, especially if they intend on treating this game like All-Star Carnival and continue supporting it long term.
Overall, it's definitely worth the purchase. I think the game probably lends itself better to the Switch than it would for the PlayStation, considering the portability and the fact that you spend the majority of the gameplay looking at the right or bottom of the screen is likely preferable on a smaller screen. That being said, I can personally confirm that the PlayStation version works perfectly well, so either purchase should work out well for you.