I've personally played through every major Assassins Creed, but Odysee, was a great step in the right direction, exploring myth, exploring the ISU and origins of the Creed.
It was bigger than it needed to be though, the loot system and leveling was way too time consuming having not maxed out after completing every DLC and there were too many times I lost track of who people were or why I was doing certain thing.
Valhalla is just incredibly exciting to me, Norse mythology is my favourite of all, and by the sounds of it they have really tightend up the story telling and progression, increased the challenge and brought it to the UK, which is a first outside of turn based strategies. Can't wait to play it.