I really like his approach to TV series, though some folks absolutely hate it. He favors long story arcs and quirky characters. A depressed vampire who looks like a hunk but prefers to sit in his room and read, for example. Or a demon who runs a karaoke bar. You can't go in expecting a realistic drama. Nor can you expect Whedon to follow the established "rules" of a genre. He even commits the greatest sin of genre television--he kills off main characters on a regular basis. This has earned him the ire of many fans over the years.
I think "Serenity" is flawed, but has great potential. Whedon had never worked on the big screen before, and he's far to busy with the camera. He lacks the maturity to simply leave the camera in a good spot and let the actors do their thing. He insists on multiple lens changes for each shot, and is *CONSTANTLY* moving. It's hard to watch on the big screen, though the action sequences are much easier to take in on the DVD. That said, there are some absolutely FANTASTIC shots in the film, including a very nice one of the hovercraft "mule" flying off the ship and several nice integrations of CGI with live action. I liked the ship battles much better than anything Lucasfilm has come out with in the past decade, in spite of "Serenity's" obvious low budget.