I really want to play a Final Fantasy game at some point, but always seem to find something else play. Same thing goes for Dragon Quest games. I could ask everyone here which game from each series you recommend, but would I actually play it? Probably not. 😔
As for a single game I own, I will probably never play Disgaea 5. It's been so long since I bought it.
SMT I actually gets really easy at a certain point of the game. Even if you run away from every encounter you should have little difficulty at beating the final bosses of the fuckhuge final dungeon. SMT I and II are both excellent games, but they have a heavy bias towards physical damage as well.
SMT if is based on the premise that you liked SMT 1 and 2, but also wish to get frustrated while playing a game like that.
Nocturne rightfully gets the reputation of being difficult, but I love the challenge of that game (and it eases off with the difficulty after Ikebukuro)
Strange Journey's gameplay is kinda mid, but the story and characters are amazing. That's what kept me going through that great game.
You've already played IV and V - I haven't.
The Megami Tensei games for the NES... MT1 is ass, but 2 is surprisingly really good. The music is great and seems better balanced than SMT 1 or 2 (I haven't finished it yet). It's kinda grindy at times though.
I heard Majin Tensei 1 is bad, but Majin Tensei 2 is a quite fun strategy-RPG in the style of say Super Robot Wars or (I believe) Fire Emblem. Great music too.
The Last Bible series is closer to generic fantasy slop than a megaten game - I guess play it if you're a completionist.
Soul Hackers is quite charming and silly, but otherwise fairly average.
Persona 1 is IMO great, but that is a minority opinion - people complain about it dislike the combat and high encounter rate. Also, the PS1 version has way better music (but the english localization is horrible) - thankfully a patch for the PSP port exists.
Persona 2: Innocent Sin has a fantastic story, but ass gameplay (on the PSP. Apparently the PS1 version is fine) - Eternal Punishment fixes all the issues, but is, well... a sequel.
Persona 3 has a great story, but is quite slow in the beginning.
Persona 4 is mostly known for its atmosphere and characters, as well as a great villain. It is however the most weeb-brained of the entire series.
Persona 5 has good, fun gameplay (if arguably too easy), but the story only gets interesting in the final third of the game. It is however
P5 premise spoiler
what I call a 1970s new left group simulator.
there's even more games but I won't talk about them, because I either haven't finished them or don't have much to say about them.