Alien Nine

It's short and ends abruptly due to being canceled mid-way, but it is gripping and truly one of a kind. The characters aren't super fleshed out, but they have enough meat to them that the end carries a lot of weight.

The animation is gorgeous. The creature designs are a bit lackluster, but the big bad "Yellow Knife" is imposing and disgusting, fitting his role in the story as an existential nightmare. I would also buy plushies of the Borgs if they made them.

My only complaint is the ending, which seems to be a common critique of this show. It ends on a bleak cliffhanger. This is because the animated adaptation ends somewhere in the middle of the manga, and was canceled before it could wrap itself up. I find this very unfortunate, as I think I'd watch a good 100 episodes of whatever brand of crazy this is.

Despite being unfinished, Alien Nine is a hidden gem of anime psychological horror. If you like mind-bendy anime like Evangelion or Madoka Magica, I can't recommend this OVA enough. It's beautiful and disgusting.