Olaf needs a thematic update
As he is the only champion that represents the idea of a 'viking' (unlike ninjas or dragons), Olaf's spellkit, and entire visual look, needs a thematic update that better represents being the one and only viking, because as of right now it doesn't feel at all like you're playing a viking champion with him. The closest thing that lets you know he's a viking is his ultimate being called Ragnarok, though its just in the name because the effects he gains doesn't at all represent the idea of Ragnarok.