Visually, this film is absolutely stunning, and the concept behind it is a beautiful fairy tale. The execution of the tale however is somewhat disappointing. I found the structure uncompelling, and the story un-climactic.
Accomodating Heath Ledger's death, the casting of Depp, Farrell and Law was actually quite excellent, and in my opinion, added to the film (if only because of the big names). The character of Tony was a compelling one, until the end where I felt the story flopped.
Overall, an interesting, very beautiful and creative film with an interesting production history. But it could have been executed better.
When watched as a 'feature film', Serenity is not much of a good movie at all. However, if watched as a high-budget episode of Firefly, then it is as brilliant as the rest of the Firefly series. Emotionally thrilling and full of good sci-fi action, and having watched the Firefly series first, I was very emotionally invested in all the characters.
A good story, a good 'episode', but not a good 'film' as such.