Its simple. This story is from Geralt perspective, and believe or not, Eredin didnt felt the need to explain all his motivations to him. Its up to player to link the dots together... or would you rather have him start talking like every single bad villain is in all movies and games just before he is defeated by main protagonist?
Eredin's motivation would be clear to you if you read books, and played previous games carefully.
I would like him to have a personality and characterization without having to headcanon the books. I know the books very well and know his motives, but it's CDP's job to make them clear in the game.
I know that a conversation like with Letho or de Aldersberg right before we kill him wouldn't work, but there are other ways.
Like people have mentioned, Eredin could have haunted Geralt in his dreams. They used this tool once at the beginning of the game and could have used it again to provide the needed interaction between him and Geralt.
Ciri/Eredin would have been even much easier. A playable flashback of the Tir na Lia events from Lady of the Lake. This would have solved most of the problems with Eredin, the Wild Hunt and Aen Elle.
CDP would just need to add:
- a conversation between Avallac'h and Ciri, in which Avallac'h is trying to convince her to make a child with the Aen Elle king.
They could explain the relation between him and Ciri, his relationship with Lara Dorren and how Ciri is a descendant and got her elder blood gene from her, what excatly going on with the white frost and why he helps her.
- a conversation between Eredin and Ciri in which Eredin tries to convince Ciri to poison the king They could explain the relation between Eredin and Ciri and why he haunts her in the game . A short conversation would have added a lot to to currently non-existent characterization of Eredin.
- a conversation between Eredin and Avallac'h showing us that they want the same (survival of the Aen Elle) but have different approaches in what way to accomplish that.
- Ciri trying to escape our of Tir Na Lia. While doing this she would find human slaves and graves. We know from Witcher 2 that the Wild Hunt abducts human children to use them as servants/slaves but this didn't play any role in Witcher 3. This would have been an easy way to implement this.
- while spending time in the Aen Elle world they could give us an in depth look on the Aen Elle (their world. history, motivations etc) and the threat of the White Frost for their world. This would help us to understand why they are chasing Ciri.
This playable flashback would solve most of the problems with the non-existent characterization of the Wild Hunt, Aen Elle and Eredin and I think it wouldn't be that difficult to implement it afterwards, because it's pretty seperated from the rest of the game. (playing as Ciri in a seperated area)
Furthermore interaction between Eredin and Ciri/Geralt is not the only way to improve Eredin's character, but he has to have some
interaction with anybody. Let him speak with his generals, or Gheel's or Avallac'h. I don't care, but let him speak with somebody.Otherwise we get what we have now. 12 sentences and less than 5 minutes screentime during 40-50 hours of story.
On a side note. I remember reading a german interview with someone from CDP last year and they talked about cut content. They mentioned two examples. One was the ice-skating with Ciri, the other one was a mission in which Geralt infiltrates the Wild Hunt. I bet this should have served as a opportunity to give them a deeper characterization. I don't know why it was cut, bit if they cut something like this they have to give us a replacement. Unfortunately they didn't and now we have a bland and shallow antagonist.
