American Gangster was two biopics and they did a disservice to Frank Lucas's story by cutting it down in order to include Ritchie's story. I'd say it's on the same level as The Aviator (which I thought was too sprawling) and a notch above Casino.
I don't know if you can even compare The Departed to those because that was a different type of movie. If you look to The Departed like it's a biopic then it's beyond retarded.