First of all, see this movie at a first-run theatre. Don't wait for a showing at a second-run theatre or the DVD. You have to see this gorgeous film in the best possible projection, because the photography is unbelievable. I assume that it was shot on film because I don't think that high-def video looks this good, at least not yet. I heard that the problem with video is that you can't use it to film things that are extremely bright (like muzzle flashes from Tommy guns) or extremely dark (like the night gunfight scenes).
The recreation of the period is great, and I doubt that 1933 Depression America looked this pristene. The bank holdups take place in large, cavernous banks with ornate walls and lots of cash, the way that banks once looked. The cars and the costumes are spotless. Even the fort-like prison in Indiana is white and squeaky clean. The gunfights are intense and expertly done. (What would you expect from Michael Mann, who did the L.A. gunfight in "Heat"?
Unfortunately the film left me a little dissatisfied because it runs off in so many directions. It explores the brooding character of Dillinger and his girlfriend (the beautiful Ms. Cotillard). It spends time with Melvin Purvis and J. Edgar Hoover, who are trying to establish a national police force (the FBI). It explores the media circus surrounding Dillinger, and the new heat faced by organized crime, who wish that Dillinger would go away. The film strikes a relevant chord, since we are now in the Depression of 2009, and the new bank robbers are credit default swaps and Bernie Madoff. For a livelier and less serious Dillinger movie, you can watch the Warren Oates 1973 film "Dillinger" on Fancast.