The opportunity to keep the film grounded in the neo-noir stylings that make the first two-thirds of the film work so well is simply tossed out the window in an inexplicable shift in tone and attitude that does absolutely nothing positive.
Without the glimpses into the darkness we wouldn't get that wonderful flash of disgust and self-hatred as Will asks for a plastic sheet so he can lie in the Angel Maker's bed.
I mean, how could you not like a film that hilariously plays on the traditional "I love you, man" dying moments and then goes on to close out the film with an animated montage of Juan killing zombies while Sid Vicious' "My Way" plays to the final credits?