Saint Young Men has a unique plot/set of characters.
Sayonara Zetsubou Sensei
DMC

Hey, they may not fit entirely, they're all what I find unique, but they're not boring (to me anyway...) at all. xD

I really recommend Pandora Hearts..
the beginning is really confusing
and the characters have depth too..

--YOUR OWN CUP OF MISERY--

Baccano!. Definitely confusing. And the characters are weird too. I highly recommend the anime. 😃

Quote from yuno19

try to follow gantz waiting room (a scanlation group)
they scanlates quite amount of weird manga that i don't even think be able to follow.

Yeah that's how found out about Gantz, Freesia, and dorohedoro. But unfortunately, I've read most of their scanlated mangas. They were all very enjoyable to read. 😃

Hey DMC looks interesting, thks Karonhioktha.

Lets see I thought Legend of the Sun Knight &Saver were both confusing & weird but once you get past the confusion there pretty decent manga

Boy Alice in Wonderland
I had no idea what was going on here after a while...I mean, I enjoyed it a lot, but half the time it made very little sense. In the sense that I really had no clue where we were in the storyline anymore. It is shonen-ai at parts, and there are some hetero smut scenes, I dunno if that's what you meant by mature! Seems like you have a good number of recommendations already, so if this isn't your cup of tea, no big loss. But it was definitely the first thing that popped into my head after reading "confusing and weird manga." xD

Helter Skelter
Omae ga Sekai wo Kowashitai nara
Fetish
Atrocious Fairy Tales for Adults
DOLL: IC in a Doll

EDIT: And I really agree with;

Quote from mu2020

the clamp universe... you got to read it very carefully and over and over again to understand it..

xxxHolic
Tsubasa: Reservoir Chronicle