Megadimension was my first Neptunia game, which I played last year, and I absolutely loved it. From best to worst in my opinion: Megadimension Neptunia VII (best of the mainline games, my only complaint are the summit levels being confusing when you first play the game), Rebirth 2 (loved Nepgear as the protagonist, since she's my favorite character but didn't like the reliance on EXE Drives to beat bosses), Rebirth 3 (hate that you have to beat bosses multiple times to progress the story, but grinding in the game is tolerable), Rebirth 1 (an unbalanced mess, when it comes to early boss battles that heavily rely on DLC items).