That said, here are some other, less highlighted reasons why 'Capote' is an interesting film:
First, Catherine Keener's role as Harper Lee, Capote's childhood friend who accompanies him to Kansas. It's really her quiet, introverted presence which provides the necessary counterbalance for Hoffman's extravagant Capote. One look from her and we know we shouldn't take Capote entirely serious. And what's more, he knows it too. (The scene on the train, which i won't spoil here, is a good example.)
Second, it is such a quiet film - i didn't think they made those anymore. Quiet as in: subtle, subdued, avoiding effects, taking its time to build up, creating suspense with looks and silences. A brave strategy by director Bennett Miller, especially for a debut feature film. There's a nice contrast too between the hectic New York parties (reminding, of course, of 'Breakfast at Tiffany's') and the silent Kansas plains and prison where most of the story takes place.
Third, this is a film based on a biography about a writer working on a 'non-fiction novel' about a real murder case. Notice the multiple layers of fiction / interpretation - which is exactly what the film is about. This is my interpretation (yet another layer), but i think Capote's crisis comes from his realisation that pure non-fiction doesn't exist, that his idea of a factual narrative was essentially flawed. On the one hand because he was manipulating the facts (he was creating them instead of letting them happen), and on the other hand because he never really succeeded in understanding the murderer's motives (the original facts). At the same time, his attempt was enormously influential.
Fourth, it's a good reason to read the book. Perhaps peeling off a couple of layers of interpretation will change my view on Capote's non-fiction ideal...