I have a really hard time believing that Serenity comes up to the level of brilliant, subtle storytelling that is Empire.
I have a feeling that Serenity is winning because it's newer and a bunch of kids who can't appreciate or understand Empire for the masterpiece it is are voting here. Either that, or Serenity is the unsung Citizen Kane of sci-fi. Which I doubt. I hear Browncoats are a pretty rabid bunch of nuts, though...
Damn show wouldn't even exist if it wasn't for Star Wars... ~600 votes now...
I think you shouldn't make any of the above assumptions without having seen Firefly and Serenity. Actually the tone of your post makes you sound dangerously like a rabid nut yourself. (I keed, I keed) ;-)
I saw Serenity first, years before I watched Firefly, and I thought it was okay, but lacked context. I would compare it to watching Return of the Jedi without having seen Star Wars and The Empire Strikes Back. But once I'd seend Firefly, and re-watched Serenity in context, I enjoyed it immensely more.
When I finally sat down and watched Firefly, I was blown away by the sheer brilliance and quality of the writing, acting, plotting, and visual effects. It is a funny, poignant series about the struggle of a group of rebels against a monolithic empire. Familiar? Yes. Was it familiar when Lucas first did it in 1977? Yes. That story wasn't new when Lucas wrote it. Would Firefly exist without Star Wars? Probably not. But neither story would exist without the vast collective storehouse of myths that underpin all stories of good vs. evil. They both tell a timeless story in a uniquely timeless way. I can safely say that Firefly belongs in the top 5 science fiction series ever produced for television, right alongside Star Trek and The Twilight Zone.
I do not think that Serenity is a better film than The Empire Strikes Back. But I love Firefly/Serenity, and I'm glad to see its legacy grow.