Just a few old ones off the top of my head.... What about:
-- Facemasks. You wouldn't see the "jacked up" hits we see today if players had to lead with their faces.
-- The streamlining of the ball. When the thing was shaped like a medicine ball, you couldn't pass it like you can now.
-- Two-way players. It was cool when players played both ways, but there's no doubt that rest and specialization on one position allows better play.
-- Modern conditioning, especially weight training. Once upon a time there was a thought that lifting made you "musclebound" and inflexible.
-- The Salary Cap. Increased parity and the difficulty in keeping a good team together.
BTW, how has fantasy football changed the game? Maybe the presentation of it, but not the game itself.