We have Zombie, Pirate, Space, and Cthulhu Fluxx. Zombie is the simplest one that we play the most and they get more complicated (cards affecting other cards/players more, etc) with some of the other decks. Personally I am not a fan of Cthulhu Fluxx but the other three are great!

Were the two moons intentional? Adds a subtle otherworldly vibe to it!