Even though this poll has closed allready, i would say '74-'78 and '04-'08 ... the start and taking off of something wonderful and magical, and the "present ones" ...
the development between these areas went from better to better, with each new theme that followed. Themes (space, fantasy) where only a spoken few fell for inmediately, while others fell for the more "open" themes as knight and pirates ...
They all have their charmes, but for me those two would be my answer (the start of my playing, and then the start of my collecting)