Anybody remember Gunman Chronicles? The shotty in that one let you choose how many shells to fire at once, from 1 to 8! If eight shells to the face doesn't bring someone around to your point of view, nothing will.
My favourite shotgun kill, though, would have to go to Max Payne (can't remember if it was in 1 or 2). Two guys lay in ambush on either side of a doorway. Diving through with the double-barrel sawed-off shotgun blazing, putting the first shot into the guy on the left side and then spinning 180 to drop the second before I landed. Even though I didn't die, I reloaded a half-dozen times just to get it right.