2. Stargate
Dean Devlin and Roland Emmerich initially conceived Stargate as a mashup of Lawrence of Arabia and Chariots of the Gods (which said aliens helped the Egyptians build the pyramids). Eventually MGM got the rights from Devlin and took Stargate to TV, where it lasted for about 13 years (chronologically) before the latest iteration of the franchise, Stargate Universe, was cancelled after 1.5 seasons of dreck and half a season of decent to good stories. What started as the story of Earth being underdogs in a secret war against aliens posing as gods ended with Earth being top dog in three galaxies within a decade and the general population still being ignorant of that fact, despite two huge space battles in Earth orbit. The problem with Stargate was that most of it was made up as they went along and interstellar politics was ignored unless it could provide a convenient and easily solved problem. As time went on, both Earth and the villains had to keep growing stronger to keep things balanced, which was achieved by upping the technology available to both sides and forcing the writers to rely on deus ex machinas to defeat the bad guys. At the same time, Earth was never allowed rally its allies and form a faction capable of defeating those enemies through force of arms or reveal the stargate, because that would make the show "unrelatable" in the minds of the writers. Rebooting Stargate isn't that tough. Keeping the Goa'uld, the franchise's initial villains, and their mythological focus is a no brainer, but dividing them into factions based on Earth mythologies gives them more longevity and helps mitigate rapid power escalation by keeping the bad guys busy with each other. Having Earth build spaceships and fighters on other planets avoids the ridiculousness of keeping the Stargate a secret when hundreds of thousands of people are involved in constructing ships that are larger than aircraft carriers and reverse engineering all sorts of alien technology, especially in an age of hackers and leakers spilling secrets all over the place. The main thing is that the right tone needs to be set something too dark and serious will keep people away, while making it too humorous and lighthearted makes it a caricature that no one will treat with respect.