If we're talking about football instead of American football, then technology has actually had little effect on the game. In fact, FIFA, the organizing body of the sport has been very resistant to using video technology, fearing that it would rob the game of the natural flow that sets it apart. However, technology has impacted training and fitness, just as it has other sports.
I agree that the protective gear is much more advanced. I was listening a sports commentator a while ago about the effect that instant replay has had on the sport. It can make umpires more confident in their class if they view it, but many purists have questioned this.
Video review has recently changed the rules in American football, slowing the game down. Coaches and quarterbacks are able to communicate via headset radios now, allowing for quicker communication.
If we are talking about "futbol" football, I don't know if technology has impacted the sport.
Helmets and more modern padding make the game safer, and better cleats make players faster and give them more stable footing. Gatorade regulates players' hydration, and various weight and exercise machines help to make players stronger and more flexible. Video recorders allow players and coaches to review practices and games, giving them the ability to correct mistakes and create game plans. Airplanes allow teams to travel faster and more efficiently, and high-priced sports cars allow the millionaire players to travel in a style which players 100 years ago could never have imagined.
Assuming we're talking about American football, the impact has been tremendous. We start with the fact that players are bigger and faster in part due to technology (better training routines, etc). Then we get to the part that is played by television and video technology. TV has changed the game and made it extremely rich. Video technology has allowed for much more in the way of complicated planning and analysis of the way that players play. This has made preparations for games much more technical and detailed.