The fourth series with Yoshitoshi ABe's involvement is by far the darkest. Texhnolyze is a true dystopia.

Plot Summary
Ichise is an outcast who gets caught in the middle of a conflict between factions in the underground world of Lukuss, where being Texhnolyzed - having ones limbs replaced with robotic ones - is a sign of status. As these factions fight for superiority in Lukuss, one girl's vision of Ichise's future could hold the answer to everything.

The Review
They don't come much darker than Texhnolyze. Oppressively dark, gritty, and violent, this series is one of the most harsh and grim realities I've ever watched unfold. There is no glossing over or sugar coating of what goes on in Lukuss.

As with the previous series (Haibane Renmei, NieA_7, and Lain), the primary theme of Texhnolyze is the disconnect of two worlds and how the gap is reconciled through the actions of the characters. Texhnolyze takes Haibane Renmei's physical separation of worlds and Lain's atmosphere of darkness and produces a hybrid of sorts that takes off in its own direction. With a longer series, the role of catalyst in the series is now split among the cast. Each aspect of trying to control and advance Lukuss lies within different characters, and this provides both conflict and progress towards an end.

Running longer than the previous three series, Texhnolyze has a much larger world and cast of characters that gives the show a very different feel to it. It's also very unpredictable to a first time viewer, such as I was, offering few clues as to where it is heading. Survival and redemption play big roles in the storyline, and as the series draws closer to the end, some questions are answered, while others are raised. The story starts out fairly linearly, then takes a turn towards the surreal as the end draws near. The final outcome is about as bleak as they come, and depending how you view it, is either depressing or cathartic.

Texhnolyze is an excellent example of a dystopia. If you haven't had much experience with stories of this type, it will be a very jarring experience. I recommend it highly with one caveat; you'll probably need to mentally prepare yourself for it. Even then, it may still take you by surprise.