Texhnolyze, Tenshi no Tamago Recommendations
Very slow, dark, and heavily atmospheric anime with minimal dialogue.
Both feature very little dialogue, ambiguous settings, dark and brooding atmospheres and depressing endings.
They really try to make you think, to the point of looking for biographies of their respective directors to search for possible connections. Heavy on the symbols, less so with the metaphors. Interpretations of both may go in completely different directions, with much depending on the viewer.