TV Shows with Uncharacteristically Dark Seasons

Both Buffy the Vampire Slayer (S6) and Mad Men (S5) have had seasons that have stood from the rest of the series as being dark/depressing.

Both shows have done a brilliant job at this by using appropriate storylines, tones, symbolism and themes. Although they these seasons may not be as fun to watch, I think they are great because in real life people have high points but they also do go through dark periods of uncertainty/depression.

I was wondering if anyone knew of any other shows that have done this.

There was a show on Adult Swim called Moral Orel. 15 minutes long, claymation, was kind of a take-off on Davey and Goliath, it often dealt with the hypocrisy found in religion and the apathy and misanthropy of adults. Not light stuff, but kind of goofy.

Then in the third season it became one of the darkest shows I've ever seen. There's some soul-crushing stuff in there and even the tertiary characters are fleshed out and we're shown how every character on this show is a deeply broken person.

Thank you for your response :)