I did rather like Firefly. I'm actually re-watching it now, and It's a lot better when you're not surrounded by people obsessed by it. You can spend less time listening to people figure out which character archetype they represent and more time soaking in the show.
Serenity was a rather standard Sci-Fi flick with the Firefly cast and setting. Not horrible, but the structure was cliched and there were too many concessions to the form. Also, they seemed to be going more epic, but without enough ideas resorted to stealing from Blade Runner, Homeworld, etc. Steal from the best, but Blade Runner has been overplayed, and quite frankly that vision of a dark future isn't really in the spirit of the Firefly universe, in my opinion.
I suspect the same raving fanatics from the first paragraph may have spoiled my attitude about the movie by going on and on about how great it was, but seriously, Joss Whedon, you can do better than that. If you're gonna do epic Sci-Fi, at least pull a Mad Dutchman Verhoeven and do a total satire of it, Robocop style. I know you have it in you. Jerk.
