Well, thanks to a kind reader I did get myself into see Serenity tonight, although the screening wasn't anything close to being full anyway.
Having seen the series on DVD, which I didn't like all that much until near the end of its run, it's hard to view the movie independently of that. Still, it probably works for the unitiated as a pretty entertaining action sci-fi movie with good humor. But more generally I'm increasingly under the impression that "that kind" of science fiction is just works much better on TV than it does on the big screen. It takes time to create an entire universe with its own rules, history, politics, technology, etc. It's generally not something all that well-suited to a 100+ minute format.
But, it's a fun movie. It would've been a good series on TV, and probably still could be.