Whedon is their god, too.
Geek/Sci-Fi mag SFX names Serenity the best science-fiction movie ever made, according to their informal poll of 3000 readers*. Whoop-de-do, you might think - everybody knows that Star Wars is the best sci-fi movie, duh! Well, you should never underestimate the power of the browncoats! Whedon fans are incredibly organized and diligent - hell, they are the ones responsible for getting the Serenity film made (financed by Hollywood based upon the strength of Firefly DVD sales).
If you don't feel like clicking the BBC News link above, here's the list of top films according to SFX readers:
1. Serenity
2. Star Wars
3. Blade Runner
4. Planet of the Apes
5. The Matrix
6. Alien
7. Forbidden Planet
8. 2001: A Space Odyssey
9. The Terminator
10. Back to the Future

If you were to ask me, my personal favourite would be No. 6 on the list. Serenity has a special place in my heart, and Lucas created a universe and mythos which has had incredible influence on everything after it - but Alien, to me, is the best made film of the bunch. (2001, while amazing - is science fiction in setting only - it's hard to judge it on the same merits as these other films)
*reflecting, perhaps, the problem with informal polls of closed member groups. The Beeb website has Star Wars leading, as you might expect amongst the general populace.