Double Face - Sennyuu Sosa Hen and Double Face - Gisou Keisatsu-hen
Are you only looking for jdrama? if not there are some good serious korean gangster drama and movies.
Last
Cruel City (the synopsis is a bit misleading, the whole girl-seeking-revenge is a mere subplot)
and I've hear good things about Friend, Our Legend
some more melodramatic are:
Swallow the Sun
Time Between Dog and Wolf
East of Eden
Giant
Movies:
New World (one of the sleekest gangland films i've seen to date)
Gangster High
not personal favorites but maybe you will like them
A Bittersweet Life
For the Emperor (basically gangland noir)