Best gangster movies other than godfathers, scarface and goodfellas

The Departed

Casino

The Irishman

Donnie Brasco

Straight Outta Compton (kinda)

Run All Night

Layer Cake

Pulp Fiction

Reservoir Dogs

A Prophet (2009) is a must see.
Lots of Takeshi Kitano movies (Sonatine, Hana-Bi)