I've had a rocky relationship with Shin Sekai Yori. A lot of the early episodes felt meandering, but usually had an intriguing scene or revelation at the end to tempt me into the next one. It didn't seem to be going anywhere, and then there was a multi-episode arc that felt like filler, or at least a distraction from the massive unaddressed surprise in the preceeding installment.
There are some really interesting ideas in the series, not to mention utterly arresting mythology and terminology - naughty children being erased from existence by "Trickster Cats", for instance - introduced in the very first episode, but to begin with it feels like a lot of worldbuilding that's quickly forgotten about in favour of a storyline focusing on something entirely different.
It's only in the last few episodes that things have started to come together, with plot threads, minor character moments and even that apparently pointless arc all suddenly being massively important not so much to the plot, but certainly to the characters and what the show seems to be trying to say.
The second most recent episode in particular had a fairly accusatory tone, pointed squarely at two of the main characters' naivety and apparent recklessness. This in addition to questions about the nature of young democracies versus the preceeding structure or other competing societal models. The show also generally seems to be warning of the unforseeable and major consequences that come about following what seem like harmless lies or rash decisions - sometimes taking years after the fact to become apparent. There've also been a few moments about racism and imperialism into the bargain, and I've not even touched on the unusual sexual politics of the society the show is set in.
There's no doubt it's a much more complicated - and adult - story than the early, seemingly confused episodes had me believing; it's a bit of a pity it takes so long to get to the point, but at the same time rushing into such heavy moral quandries could have been even more off-putting.
I can see more than a little bit of Lain in the philosophy and even the art style, but really I can't think of anything quite as multifaceted as Shin Sekai Yori; if you've got the time to watch the fourteen episodes released so far, I highly recommend it. I would urge you to watch them in quick succession too, otherwise the slow pace might put you off altogether.