For me, it's almost everything.
The technology of movie making, especially when during the 1970's, GL managed to pull off all those space fights, AT-AT attacks, etc
The story line - good vs evil, through a sci-fi theme, and not forgetting something as mystical and bizarre as
The Force
The easter eggs in the movies
The music - enough said
Natalie Portman, Natalie Portman, Natalie Portman......
Last but not least, the toys
Even with the bad vibes on the prequels, I've thoroughly enjoyed them