Complex sentence: Kim Ki-young's mature style first fully expressed itself in his best known film, "The Housemaid" (1960), which features a powerful "femme fatale" and is widely considered to be one of the best Korean films of all time.
Split into simpler sentences: Kim Ki-young's first expression of his mature style was in his "The Housemaid" (1960), which featured a powerful "femme fatale" character. It is widely considered to be one of the best Korean films of all time.