At the end of I, Vito has become a gardener and a grandfather, a man who plays with his grandson. Vito has found some sort of meaning or redemption at the end of a long path of criminality. Michael, on the other hand, dies alone, not even a young child to mourn his passing.
In the novel, Vito's dying words were: "Life is so beautiful." The last words of Michael's life probably were "arf-arf" from that little dog who was his final companion.