Cam Clarke's performance as Kratos. Consensus seems to agree that he does better than the original voice actor.
The majority of the fight scenes in the OVA's are done really well.
Sheena right after Volt kills Corrine, who threw himself in front of her to protect her from a lightning blast. She proceeds to stand up and demand Volt to make a pact with her.
"For the sake of everyone who risked their lives to protect me... Volt! I DEMAND your power!"
The first time you have her summon a Spirit would also count.
The first trip to the Tower of Salvation. It's simply unforgettable. Add in some Big Damn Heroes moments (from the party) and then the Renegades to a epic Boss Rush, with amazing Music. (Let's not forget, this is where the game shifts gears from otherwise generic JRPG to something much more epic.)
The OVA makes the entire final fight this for Mithos, as he gets to show off exactly what happens when you fight a four thousands years old Magic Knight who hasn't gone soft. The party barely manages to land a hit on him and even when he decides to finish things in a one-on-one swordfight against Lloyd, he only loses out of choice.