The thing I thought was most interesting about White Heat was that it didn't waste a lot of time on establishing character. By 1949, all you needed to do was cast James Cagney and the audience would do the rest of the work.
I mean, Cagney's still great and you can't take your eyes off him when he chewing up the scenery. But they save a lot of time by not telling us how he's a vicious sociopathic monster. He just is.
I think I've seen all the essential Cagney gangster pictures now. I should probably hunt down some Paul Muni now, because he's always listed along with Cagney and Edward G. Robinson in these Warner Brothers histories but I've never even seen the original Scarface.