the official anime is out (ep1 on 4th Oct) and its worth watching is. Animated by Madhouse, so animation quality is superb its has alittle extra scene compare to manga as well

Kaito Ishikawa (Zankyou no Terror, World Break) as Genos
Makoto Furukawa (Golden Time) as Saitama

Aoi Yūki (Rokka no Yuusha) as Senritsu no Tatsumaki (Tornado of Terror)
Daisuke Namikawa (Gantz) as Butagami (Pig God)
Hiroki Yasumoto (Bleach, School Rumble) as King
Katsuyuki Konishi (Guren Lagan) as Tanktop Master
Kazuhiro Yamaji as Silver Fang
Kenjiro Tsuda (K) as Atomic Samurai
Kousuke Toriumi as Senkō no Flash (Lightspeed Flash)
Mamoru Miyano (Ginga Bishonen  ) as Amai Mask (Sweet Mask)
Masaya Onosaka as Pri-Pri-Prisoner
Minami Takayama (Conan) as Dōtei (Child Emperor)
Saori Hayami (   do i need to say more?) as Jigoku no Fubuki (Blizzard of Hell)
Satoshi Hino as Chōgōkin Kurobikari (Superalloy Darkshine)
Takahiro Sakurai (Spinzaku  ) as Zombieman
Tesshô Genda (Seto no Hanayome) as Metal Knight
Wataru Hatano as Kinzoku Bat (Metal Bat)
Youji Ueda as Kudō Kishi (Drive Knight)
Yūichi Nakamura (Clannad, Macross Frontier) as License-less Rider
Yuji Ueda as Banken-man (Watchdog-man)
Yuuki Kaji (Accel Time, Aquarion Evol) as Onsoku no Sonic (Speed of Sound Sonic)