I recently got to see this in the Dreamworks theater with my friends Shane and Frankie (thanks, Shane!). It was a movie Shane and I had been really looking forward to since they first announced it.
Unfortunately, it was a let-down. The easiest way to critique it is to call it a weak version of Heat (one of my favorites, by the way). Heat gave you a fascinating look at the lives of the two leads, making them real and sympathetic characters. Public Enemies was really lacking in that department. I didn't connect with Dillinger or Purvis, or anyone else. I don't think it's the fault of the actors. The script was either lacking from the beginning or hacked during production.
Despite the lack of emotional connection, there are a few good things to be said about the movie. For one, Mann once again did not disappoint in the action and sound-design department (see also Collateral and Heat; Miami Vice also qualifies, but it's a terrible movie). The shootouts are loud; they look, sound, and feel very realistic. Furthermore, despite some shaky-cam hand-held work (die, trend, die!) and the occasional obviously digital picture quality that made you miss film grain, there were some beautiful compositions. The opening in particular has a great location that makes for some cool looking minimalist framing. Costuming and locations, of course, were all good. It was funny seeing the British actor who played Tommy in Snatch as Baby Face Nelson. And Faramir as a nameless henchman who must have been offed at some point.
To sum up: disappointing. Worth it if you have a good sound system for the action scenes.