The rendered introduction movie in the first game is a retelling of one of the first short stories, published way back in 1991, and it's an excellent, action-packed sequence staying almost entirely true to the original story, down to each individual blow.
Killing Azar Javed at the Manor not only gives Geralt payback for Kaer Morhen, if you spared Berengar, he returns to help finish Salamandra once and for all.
In the first major quest hub, if you chose to save the witch that's being hunted by the villagers, Geralt delivers an awesome speech towards the villagers. Did I mention he scares off the priest by pointing his blade?
Geralt: You have two options. Wait until I leave and then murder Abigail. But then I'll come back. I'll slay every lice ridden peasant, anything that moves and can't climb a tree. Or, you can lead honorable lives, clear your conscience, start again. Like humans. The choice is yours.
The fight with the golem.
After escaping the turmoil in Temeria, Geralt resolves a conflict between a group of sentient amphibians and a small human village. For his actions, the Lady goddess of the Lake knights Geralt, gives him a magic sword, and tells him to go face his destiny. That's right, Geralt is now King Arthur.
Actually, the sword in question Geralt receives is a silver blade called Aerondight. "Arondight" was the sword given by the Lady to a bit different knight, effectively turning Geralt into Lancelot. Which is actually even more appropriate.