New narrow-band images of NGC 4151, taken in excellent seeing conditions with the 4.2-m William Herschel Telescope are presented. These reveal a wealth of detail that can be used to test models for the anisotropy of the narrow-line region. From forbidden O III (4959, 5007)/H-alpha line ratio map, three important features are identified: (1) a jet-like linear structure that extends in a series of relatively high-ionization blobs along PA of about 50 deg out to a radius of more than 15 arcsec to the south-west and 5 arcsec to the north-east; (2) a lower ionization halo surrounding the linear structure; and (3) a band of lower ionization or higher obscuration through the nucleus, almost perpendicular to the linear structure.