I used to be fan of bleak, dark & melancholic anime - while most of these might not be "dark western", some are for sure a downer. Here's a few I like.

I recommend Texhnolyze as it's... very slow, and a little boring to watch, but that by itself maeks depressing and interesting. Just as reflects teh world teh main characters live in.

Ergo Proxy has always ben a favorite of mine!
For sure more sci-fi. What is life without Pino!

Monster, i been meaning to read teh manga as it´s 10+ years since i saw teh anime. Bleak, yeah? Dark noir - no.

Just to name a few; The Big O, Casshern Sins, Haibane Renmei, SoulTaker, Angel's Egg, Megalo Box