This is Christopher Walken's movie, more than De Niro's.
I watched it again yesterday after many years and I just realize that the pivotal moments I remembered from the movie, it was all Walken. His transformation was impressive, tangible. The same way the Gladiator belonged more to Joaquin Phoenix than to its hero, Russell Crowe. Walken's performance just blew me away.
http://www.youtube.com/watch?v=PjC-tI_QKgw