I've just finished case 6. Really enjoying it! I forget how much I love Platinum games. The further I've gotten through it, with more legions and more abilities and skills all unlocked, the better my rankings are - although I'm still wildly inconsistent (I think in every chapter I've gotten multiple Ds and S+s).
I also just love a game that veers sharply from po-faced dramatic (if predictable) sci fi, to feeding cats and putting a cardboard box on your head in the locker room.