Nowadays people buy games because of sexual innuendos and "moe" instead of gameplay or story, it's kind of obvious why the video game industry has been struggling so much.
Nobody in their right mind actually buys and plays a game solely for sex and moe, unless it's an eroge. Neptunia isn't known for being the crown jewel of RPGs, and I will never claim that it is, but that does not mean I can't appreciate the series for its art. Notice how many said they hadn't played the games but would watch the TV show? That's because the premise and characters are interesting.