Jungle Nasus is alright his ganks are decent if he has someone to follow up when there over extended, examples like Twisted Fate stun, Darius pull and Graves Smokescreen to block vision. work well with him. You follow up when there stuned or form of cc to apply wither and 50% chance you can a force flash on the enemy or possibly get a kill. I wouldn't use him vsing an enemy team with a lot of escaped like Ezreal's flash, Ahri's ulti and Garen q (you cast wither he can use q boom no more cc on him.) Along with Cleanse and QSS. He also loses a lot of Q farm doing that so it makes it hard to go on a one shot ownage who let the dog out rampage late game. Thats point of view.
The only thing nerfed about him was the attackspeed slow, which only went down from unbelievably broken to very strong. All the dragons are still yours, you still get decent Q stacks if you last hit big monsters when convenient, and you still scale into the tower-crushing god of the rift as the game goes along --- And then John was a zombie.