Just to clarify, series of films like Indiana Jones, Jurassic Park, Back to the Future etc arent being counted as trilogies as they arent a planned series or they dont tell a single coherent story.
...and yes I know the DVD sets for Indiana Jones and Back to the Future CALL them trilogies, but thats just to make you pay more
Other 'not quite trilogies' include The Omen Trilogy, The Scream Trilogy, Die Hard, Blade, Rambo, Robocop, Exorcist and the '...of the Dead' Trilogy
BTTF is the most debatable, but you have to draw the line somewhere
...and yes I know the DVD sets for Indiana Jones and Back to the Future CALL them trilogies, but thats just to make you pay more
Other 'not quite trilogies' include The Omen Trilogy, The Scream Trilogy, Die Hard, Blade, Rambo, Robocop, Exorcist and the '...of the Dead' Trilogy
BTTF is the most debatable, but you have to draw the line somewhere