There is a really deeply spiffy interview with Joss Whedon here which is worth your time. Lots of in depth discussion about his contribution to films in general, including Toy Story, Speed, Wonder Woman and of course Serenity, with no significant spoilers that I’ve noticed.
EDIT: …and Batman, and Global Frequency, and Iron Man, and Powers, and….
EDIT 2: …and House, and Veronica Mars… phew! Long interview.