Mentally stimulating anime (Whiny, demanding anime request! :D)?

[Noah]

An anime that totally fits into your category (and I love that category), would be:
Steins;Gate
http://myanimelist.net/anime/9253/Steins;Gate

Summary:
Steins;Gate is set in the summer of 2010, approximately one year after the events that took place in Chaos;Head, in Akihabara.

Steins;Gate is about a group of friends who have customized their microwave into a device that can send text messages to the past. As they perform different experiments, an organization named SERN, who has been doing their own research on time travel, tracks them down and now the characters have to find a way to avoid being captured by them.

Something that totally focusses on exploring human nature, and I'm SURE you'll love this is:

Welcome to the N.H.K!
http://myanimelist.net/anime/1210/Welcome_to_the_NHK!

Summary:
Satou Tatsuhiro, 22 years old, thinks that everything that happens around him is a conspiracy. He even figured out who is behind it all: The NHK, an evil secret company.

"When you think anime, you think otaku. When you think otaku, you think people that dislike other people. Those people become hikikomori (people who shut themselves in)". So Satou manages to uncover the plot of The NHK (stands for Nihon Hikikomori Kyokai), after three years of shutting himself in (and rapidly approaching the fourth).

In reality, he is nothing more than a NEET (Not in Employment, Education or Training), desperately in need of a cure from that "disease". He wants to break out from the curse, but going out and getting a job is frightening enough for him. That is until he gets selected for a "project"; it is a plan to help hikikomori like him in facing the reality of this world.

You can check the "Recommended" tab for both of them for more anime like them.

I wouldn't be too scared to check out Code Geass though, it's "battle of wits" comes close to Death Note, and it's debatable who is more intelligent: Lelouch or Light (and it doesn't have that much more episodes than death note)

I'm sure you'll love Steins;Gate, it fits your categories PERFECTLY, I swear it on my otaku soul!