In addition to its mind-bending plot, action, and imagery, Kurozuka has a cast full of top seiyuus. Here is a character/seiyuu page showing little pics of each character, with a pic of their seiyuu and info about his or her past roles.
Paku Romi -- Loran Cehack (Turn A Gundam), Edward Elric (FMA), Osaki Nana (NANA), Teresa (Claymore)
Miyano Mamoru -- Kiba (Wolf's Rain), Tamaki (Ouran HS), Light (Death Note), Setsuna F. Seiei (Gundam00), Zero (Vampire Knight)
Nakata Jouji -- Alucard (Hellsing), The Count of Monte Cristo, Van Grants (Tales of the Abyss)
Kuwashima Houko -- Sango (InuYasha), Shuurei (Saiunkoku), Clare (Claymore)
Fujiwara Keiji -- Nohara Hiroshi (Crayon Shin-chan), Holland (Eureka 7), Shuu-chan (Honey & Clover)
Irino Miyu -- Sena (Eyeshield 21), Syaoran (Tsubasa Chronicle), Saji Crossroad (Gundam00)
Inoue Kazuhiko -- Dusty Attenborough (LoGH), Nefee/Nereis (Banner of Stars), Gorou (Moonlight Mile)
...with more to come.
For a long time the top three in the list were the only ones named on the show's official site. It appears they cobbled together the rest of the cast near the last minute. Maybe that was when some top seiyuu knew for sure they had time.
Click on the image to go to the character/seiyuu page: