Well, both of them are "Torino Vermouths" (i.e. spiced wine drinks infused with herbal extracts, Torino style), but Cinzano seems to contain less aromatic additives compared to Martini and the resulting taste is closer to wine than that of Martini.
There are at least 6 recipes for vermouths I have (Torino vermouth, Piemonte vermouth, Venetian vermouth), unfortunately, all of them include ingredients not available to me (like "dried gentian" etc.).