Inject new game ++ into your veins
Persona 5 Royal got the Persona 4 Golden treatment.
Hardly any additional content, but a whole new endgame dungeon to stretch the story out.
I personally will be getting Royal day one, and even then I just finished my 5th play through of the game.
It's entirely subjective of how much you wanna run Persona 5.
I enjoyed the game enough to do such things, but now I'll get to re-play it in Royal with the added characters and see what happens for myself.