We saw this movie partly because it was filmed here in Chicago, partly because Johnny Depp stars in it, and partly because we usually like gangster movies (we recently watched namesake Public Enemy on DVD at home). As it happened, there wasn't that much Chicago background in it (I think a lot of the scenery was digitized), and--on the whole--the movie was a disappointment. Far more style than substance.
Which is hardly a surprise, when the movie was directed by Michael Mann, but we have liked some of his movies very much (e.g., Collateral, The Insider). Those movies had better plots, though, and more interesting characters. Depp does his best with Dillinger, and Marion Cotillard is wonderful as his love interest--when these two are on screen together, you're happy.
But mostly the movie is a grim, violent, stylish spectacle. There's little to care about here, though it's very pretty to look at.