Every episode has stolen my heart so far. After rereading the corresponding chapters, it is apparent that they changed certain scenes, but they are sticking to the main themes of the story that the oracle mentions.
The ending is a new scene. I always wondered how the gods first reacted to Medusa's head. It was fun to see a little bit of how they probably reacted. The scenes that they add to the series feel like they are giving older fans new content.
One thing that I noticed was instead of Annabeth volunteering for the quest she was chosen by Percy. We later learn that it is because of what the Oracle said to Percy in the prophecy. Due to their previous interactions, Percy is unable to see a future where he can be friends with Annabeth. I really enjoyed this change because it opened a door for the two see that they can trust each other.
I am glad that they are focusing on Percy's feelings about his father and his lack of interaction with him. It is important for the story when we learn about the impending betrayal.