A very good experience, I do think the game drags the most in the middle section, in the 4th "stratum" (worlds in this game), where you have to go up and down multiple floors hunting for event flags.
The story is the main draw here, though you should definitely heed the content warnings for it, it gets quite uncomfortable and dark, but is ultimately worth it.
The exploration loop is quite fun, but I feel the combat is fairly simplistic, boiling down to autobattling for most fights.