I've been asking myself for a while now why I'm reading something that's basically "Noryoku Gakuen Gekokujo but technically not fully a hentai", and I've finally figured it out: it's the comedic banter between the ghosts (and I'm including totally-not-Mordred's floating soul in that category, because she seems to have settled into a solid role in their group dynamic now).
That's the special thing this manga's bringing to the table: the humor of this strange group of friends, and the way that the mangaka's taking advantage of the fact they're ghosts to allow them to kibbitz and argue about things under any circumstances. That's what this has that the straight-up hentai version (or non-H manga version of this kind of revenge story) lacks.