Actually, his performances in all five of his movies stand out and one can't help but wonder if he'd lived longer what his film future would have held. My guess would be more pairings with Al Pacino and I'd be willing to bet that Quentin Tarantino would have pursued him for a role or two.
John Cazale's life ended just when film audiences were starting to recognize him. Surely his track record of being in great films would have ended, but just think of the lesser films that would have been so much better just to have had his presence.
I often wonder what kind of career Joe Pesci would have had if John Cazale had lived, as I could easily see Cazale in Goodfellas or Raging Bull - or for that matter, Home Alone. We'll never know what would have been. The only thing we know for sure is that the movie world is blessed to have had John Cazale - if only for a short while.