For the most part my experience is that the anime that hurls the most nudity and blood at the audience tends not to be worth watching unless you simply want to see naked, bloody cartoon characters. It is often a way of saying, "the story and characters are bad, here's something to look at to make up for it."
Elfen Lied is an oddity in that it contains oodles of gratuitous nudity and stomach-churning violence, yet the story is genuinely interesting, making you care about the characters and wonder at who the monsters really are.
The reviews I've read here generally take the nudity more to task than the violence, the idea being that the nudity fails to propel the story whereas the violence underscores exactly how dangerous the tentacled girls are. On the surface this is a reasonable argument. Certainly the nudity is irrelevant to the narrative, failing to in any way define the characters, and in the case of girls chained nude in government labs, it feels quite exploitative (although one could argue that it was a technique meant to reinforce the inhuman status of the subjects to the lab's employees).
The violence, on the other hand, has a horror-movie effectiveness to it. And I'll admit that a lot of the reason I didn't like it is that I'm squeamish (it's not nearly as hard to take in the manga). But the truth is, the series does not just efficiently show the damage, it glories in it. It is violence porn, like those Mortal Kombat games where blood spurts out in geysers. Violence was necessary, but the degree of violence simply was not.
I think the reason you don't see much nudity in great anime, and generally less gore, is simply that the makers have faith in their story. Elfen Lied is a series that hedges its bets, and by doing so, it falls short of being the series it could have been; one that dared to stand entirely on its stories and characters.