The plot of Y: The Last Man is a pretty straightforward apocalyptic tale: one day, every man on earth drops dead, blood gushing from their noses and mouths, leaving no one behind but women, and one man, and one male monkey (his pet -- a helper monkey he's been training). The setup rapidly progresses into a gripping, funny, sad and lovely tale of the post-apocalyptic world.
Book five seems to be firmly on the downhill side toward a conclusion, something we don't get nearly often enough in the world of funnybooks. The art is tremendous, too -- there's a page 60 showing a teenage girl storming away from Thanksgiving dinner that is possibly the most expressive bit of comic book art I've ever seen. Book 5 Link, Book 4 Link, Book 3 Link, Book 2 Link, Book 1 Link