The story takes place in the fictional Japanese metropolis of City Z. The world is full of strange monsters that mysteriously appear and cause disasters. Saitama, the protagonist, is an exceptionally powerful hero who easily defeats the monsters or other villains with a single punch. However, due to his overwhelming strength, Saitama has become bored with his powers and is constantly trying to find stronger opponents who can fight him.
http://www.imdb.com/title/tt4508902/?ref_=fn_al_tt_1 currently 9,6 on IMDB
http://myanimelist.net/anime/30276/One_Punch_Man currently 8.83
I highly recommend you check it out if you like action anime.