If Nunu ends up like I think he will, he is going to be the perfect example to how a tank should be:

Low damage overall, but alot of soft CC on a very low Cooldown.

When you ignore him in Teamfights, he aint gonna kill your team, but his snowball spamming will slow your team and root them, making it hard to actually get to the priority targets on the enemy team.

So you either kill him or he will annoy you the whole fight.

Ultimate for added pressure, since its the only spell that can deal alot of damage, but you can decide to use one of your Disable effects to stop it, of course in that case, you wont have it for... lets say... the Assassin.

Perfect example for how to make a tank champion.