I will briefly try to explain the merit of NieR/Drakengard from my perspective.
D1:
The merit of this game are the storytelling and the characters. I cannot think of an RPG, J or not, in which pretty much the entire party are complete assholes with almost no redeeming qualities. The main character rides a man-eating dragon, but even the dragon is at times revolted by the bloodlust of her rider... you also travel with a pedophile, a little boy ( ... ), and a child-eating elf. And some other jerks. The story is completely fucked up that needs to be seen to be believed. One could argue it's "so bad it's good" but it's not really bad it's just... well, it is hard to explain. The key milestone this game did few others do is the way the game unfolds: on your first playthrough, the game is told as the story people remember after. Then, for each further ending (which require altered/extended playthroughs) the real story is revealed, and you can see how, in the retelling of the story, people white-washed the main character and glossed over his cruelties, for instance. Seeing the true stoy and true ending are a kick in the kidneys.
D2:
This game does not exist.
D3:
This is similarly fucked up. People don't like it as much as 1 but it has spectacular music.
NieR:
NieR is the most depressing game in existence, with a soundtrack considered to be, depending on who you ask, the best in all of video gaming. While that is debatable it is definitely up there. It's still a stand-out achievement: every single song is incredibly sad, but in different ways, with that faint hint of hope, that is, ultimately, snuffed out. Perfect for depressed people! The entire cast is likable, yet the story is just crushing. It's also the least anime since you play some ugly dad. Like in D1, successive endings peel off layers of the story until the whole, heart-rending truth is revealed.
As a whole:
The real appeal of these games is Yoko Taro's insane genius. The man will spit on his playerbase in order to tell a story. That's something I can admire. Imagine Hideo Kojima. But now, instead of some insane, crazy ending that has people scratching their heads, imagine if, at the ending, someone extended you a giant middle finger, then promptly punched you in the face. The man is not afraid of 'not caring.' He was jobless for a while because of this. The story is what matters to him, and telling it through gameplay mechanics in an admirable way. One example from NieR: there are all these lame, pointless side quests. The whole point is to ram down your throat how much he hates lame side quests. Or soundtrack of D1: it's nothing but a horrible cacophony meant to instill the horrors of war - and indeed, the entire game involves slaughtering thousands upon thousands of people, most of them innocent. Or the boss fights in D1/D3 which involve a complete genre change and downright blatantly deliberately unfair sequences. Or, perhaps the best thing he ever did, how reaching the last ending in NieR requires deleting your savegame for good, further rubbing in all those pointless side quests you did.
Basically, it's interesting to watch the writings of a very depressed, incredibly alcoholic madman who hates his players so much that it ends up feeling like love.
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