The Cylon Plan was to kill all the humans, they just screwed it up because Cavil had issues with the Final Five. He wanted them to be punished and wanted to draw out their punishment as long as possible, but then it was too late. It fits into one of the themes throughout the show that there really wasn't much of a difference between the humans and cylons. Cavil, despite wanting to be a machine, was just as petty and obsessed with revenge as the humans he hated. It isn't the show's fault that it didn't live up to some fans expectations. I don't know what you could have wanted it to be.