All You Need Is Kill
The premise was interesting, but somehow, the actual story fell short.
Boku Dake Ga Inai Machi
Had an excellent anime adaptation, and the manga was very good as well.
Gantz
This is one of my favorites. Dark, twisted, sexy, and completely crude - just the way I like a seinen work. A long one, but def worth the read.
Homunculus
Something so delightfully twisted that you'll be able to lean back in your chair and say "Aah".
Omoide Emanon
Very calm. She is able to remember everything about the earth. I actually have to reread this. She's seen things come and go. It feels so beautiful, like a wind that slowly takes you away.
Akira