Dark and moody, noir, but not excessively angst-ridden. The world is not universally sinister. The art can balance graphic novel melodrama with a sense of a story well told. Nothing "cartoony" about it, though an anime-based style might work.
Greyscale, perhaps with very deliberate use of color.
Some humor; some beauty.
Not macabre or surreal, although it can be playful and magical realism is not an impossibility.
Generally realistic (depending on your definition), though not without a sense of the artist’s particular style. A complex story is to be told. The story must focus both on individual expression/facial detail and moody cityscapes. Creative and expressive layout is a must.