Here's a couple that spring to mind:
Michael Corleone in The Godfather Part III: He dies of old age, no shocking hit or crossfire murder. That's pretty anti-climatic for a genre defining character who made shitloads of enemies and even pissed his own family off.
Scott Summers in X-Men The Last Stand: He more or less dies off screen and very little is said about him for the duration of the movie.