The film is not particularly 'slanted' or 'one-sided' (although it's fairly easy to figure out where the filmmakers sympathies lie), and doesn't try hard to 'demonize' any individual (although some subjects do a pretty good job of demonizing themselves). For example, many scenes that could be nothing more than dry transcript reading are in fact voiced by an actor over an image of a moving reel tape player as well as the printed materials. It's firmly in the form of a 'documentary', but with a much larger team and budget and higher production values than that category label might at first lead you to expect.
'Casino Jack' is about the Jack Abramoff lobbying/influence-peddling/fraud scandal.