Not only have I completed it, but I've sunk a heck of a lot of hours, bought and played through the DLC, and gone into reading the novellas and manga side stories also.
The game will likely continue to polarise you, if you don't end up outright hating it, by the sounds of things.
Indeed, she has no remorse for murder, and there's a strong point to this, but you're going to have to play through the whole thing (all 4 endings) in order to figure out why.
Actually, it gets even deeper than that. There's a shit load of questions that remain unexplained, and I'm having a great time discussing them on a Drakengard 3 dedicated forum.
Drakengard 3 is, without doubt, the most enjoyable storytelling experience I've had this generation, along with the spinoff 'Nier'. Much of the enjoyment comes from the complexity of the story (which initially comes out as feeling incomplete and a mess, until you realise that the story has been made deliberately inconsistent and obscure, and relies on the the gamer's interpretation to fill in blank spots in the story).
But, make no mistake, this is a game that demands your effort in order to appreciate to it's fullest. Sadly, not included in the main game, but on the internet there is a bunch of novellas that explain the stories of each important character prior to the events of the game. These are actually essential reading if you want to understand the motives of each character.
They've been uploaded to the Drakengard Wiki. Another website (and a REALLY fucking awesome one at that!) called 'Kid Fenris', also gives a rather deep analysis of the 2nd boss, Four, on his website (best to read after you've defeated her)--
kidfenris.blogspot.jp/2014/06/dr ... -four.html
-- going to show that there's much more to the characters and story than what meets the eye.
D3 has something else in common with Panzer Dragoon in that there is greater depth and detail to the story, when you take the time into observing it's world, than when first approached.
Most people think Panzer Dragoon is nothing more than a bunch of shallow rail shooters, and an RPG, with a weak and super-streamlined story, but we all know that in actuality, a lot of thought and effort has been put into it if you observe and read between the lines.
The Drakengard games are exactly like that, but actually even deeper than the PD series has ever been. They strange, fascinating, and very different from just about any other game in the industry, and whilst very flawed, they have gained a cult following for their differences, warts n all.
Much of the fun with Drakengard 3 comes from reflecting upon the seeming strange and inconsistent decisions made from how they present the story, trying to figure out how much of it was intentional, or flaws due to budget constraints and other disadvantages.
Like I said, it sounds like the game hasn't grabbed much of a grip on you (although I've read reviews that have said that the game actually gets a hold on people much later in the playthrough). But I think, or hope, that you will at least appreciate how this game is fascinatingly different from anything else out there.