He is so much better in Non-Gangster Roles than Gangster Roles..

In Mafiozo Roles - except being tough and brutal,there is zero emotion.
Noodles in OUATIA and Jimmy in Goodfellas are pretty much same character in different variations. His best gangster roles were Mean Streets and Casino. And in both,he's not even typical gangster. Punk kid and Casino manager.

His best work:
The Deer Hunter , Cape Fear , Raging Bull , Midnight Run , Taxi Driver , Fan , Falling in Love , The King of Comedy , Awakenings