This game poses a simple question: how good is a game with excellent gameplay and terrible plot?
And make no mistake — the gameplay is excellent. This is the most fun I think I've had in an open world JRPG, and the first ten hours were spent agog with joy. The combination of the dangerous power curve for which SMT is infamous and a truly open world where exploration is both dangerous and valuable is so, so, so much fun. You're spending around two thirds of your time traipsing across one of four open world areas that grow in complexity & difficulty — culminating in the final area which feels like a true test, an area where you have to spend a solid two hours running away from everything in sight and gleaning power-ups until you can start to challenge some of the enemies within.
The problem, then, is the plot. Note that I say terrible. Not "completely non-existent", like with a roguelike; not pleasantly mediocre, like [[Steamworld: Quest]] or [[Link to the Past]]. The game's plot is bewildering and clearly half-written; entire plot arcs build and resolve in the span of a single cutscene. You do not care about any of these characters; none of their actions cohere. The alignment system (an SMT mainstay) is not just obtuse but pointless; it exists in a vacuum, and the One Big Choice you make only influences the last 5% of the game.
I had fun playing the game, even if I was happy to be done with it (to be honest, most 50 hour JRPGs instill the same effect in me!) But play it if you want to level up a bunch of demons and have fun JRPG gameplay. Ignore it if you want to actually care about the plot.