In Harry Potter lore, a Thestral is a winged beast of burden resembling a horse - if you haven't personally seen a death. Once you have, you see them as they really are. Still oddly magnificent, they become in your eyes a skeletal dark steed. You will now never see them as regular if winged horses ever again, and you have a hard time conveying to others what they now look like to you.
I think with this in mind, I may have figured out one of the dividers between Elfen Lied fans and at least some of the haters or at least the dismissers. In short, if you haven't been bullied, you cannot see that EL is not as far over the top as some claim. If you haven't experienced that kind of deep down, be-afraid, you-are-hunted, you-are-not-wanted-and-never-will-be, half the room starts giggling and walking over to start in when you arrive kind of bullying, you will declare the series what seems to be the cool kids mantra: Emotionally manipulative.
So for those of you fortunate enough to only see a winged horse, great for you. But for the rest of us, we see something you don't or can't, and all the decrying you do sounds like crying to us, because something you don't get is gotten by someone else. I'll end this calm rant with the consideration that, by the time both series ended, the bulk of their casts could see the thestrals as they really were, in the aftermath of God-wannabes cut down by their own fearful schemes.