DC has done some really great, at times thought-provoking non-“superhero” miniseries over the years. Many of them were published before Vertigo was established, though Vertigo has had some good series that came and went with little to no fanfare. I’m thinking series fewer than 12 issues.
Two of my favorites are:
Tailgunner Jo (DC 1988, Peter B. Gillis (w), Tom Artis (a), six issues)
We3 (Vertigo 2004, Grant Morrison (w), Frank Quitely (a), three issues)