Heat
Michael Mann's probably my favourite director of all time. I don't know what it is, but his films always seem to have this extra indescribable something that other directors, even really bloody good ones, just don't bring to the table.
As for the film in question, it's been a while since I last saw this. While I wouldn't say it's my favourite Mann film, there's no denying it's probably his magnum opus. And come on, Pacino and De Niro acting on screen together for the first time... (Godfather II doesn't count, they were in separate time periods lol.) And they're just the tip of a really awesome casting iceberg; everyone excels in their role, and there are a lot of roles. Plus if the shootout in this isn't the greatest ever put on film, it's certainly the greatest sounding.