Though I've only played a good few matches in both the Beta and full game released as of today, I saw no balance changes made to Níðhöggr. He's a character too overpowered compared to the rest of the cast. His axe throw ability hits and does damage, then stuns enemies upon returning to his hands. I haven't played him so I don't know the cooldown times on his abilities, but they seem fairly short and too overpowered, especially his lightning storm ultimate, it does far too much damage for an ability that's description explicitly stated stuns, and lasts way too long.
I feel his abilities need longer cooldowns and weakened damage, and that would make him a more fair to fight character.