Nunu is not bad in Dominion.
Max rank Consume and 1 autoattack (2 autoattacks later in the game) will kill a tank minion. What's significant about that? It lets you push. Consume has 1:1 AP scaling on its heal, on top of a base heal of ~300. Consume deals 900 damage, to which spellvamp applies.
Blood Boil buffs an allied autoattacker with 65% attack speed. That is a lot. Because it lasts 15s on a 15s cooldown, taking a single rank in BB means you don't need to upgrade your boots until you want to.
Ice Blast has 1:1 AP scaling, chunky base damage, and a low cooldown. It slows by a murderous 60% for 4 seconds. Add some CDR and you can perma-slow someone and fly them like a kite while you chunk them down with successive snowballs.
Absolute Zero is hard to use. That's because when you use it well, it kills people extremely hard. It has 2.5:1 AP scaling, on a base _1125_ damage if you get the full channel. That sounds like a big number. It is. Absolute Zero can one-shot people who don't build defensively, and cut in half the health bars of people who do. Wait for your opponent to use their flash, their stun, their blink, then run up right next to them (BB and Ice Blast let you do this) and make it snow.
Finally, Nunu has high base tanky values. He hits ~2400 health at level 18. This is 500-600 more than some champions.
Nunu is not Panth/Poppy/Kass/Darius-tier. Few champions are. He's still a good pick if you know what you're doing - which is the state of balance all champions should ideally exist at. He can lane top or bot. He does well in 1v1s and 4v4s.
To play Nunu well you need to play to his strengths. I don't want to spell out a build, but what you don't need is a ROA. What you do need is 30-40% CDR, some mana or mana regen to ease you through the early levels, as much AP as your yeti can carry, and as much or as little health, armour, and MR as you feel like you need.
have not gone into any AD Nunu build options. This is not because they do not work.
Moon-krug, and good luck.
PS I posted this into the other thread by mistake.