Nunu & Willump is now a CC monster that can get around the map very fast, has amazing neutral objective control, and zone control. In short they took everything that made old Nunu & Willump good and added features that make him even better.

Important things to note is that all of his ablities now either do damage or enhance his damage whereas before he was limited to his ult, AAs, and his snowball for damage.

His new passive, Call of the Freljord, is basically Blood Boil except it now makes his attacks cleave which helps with taking down jungle camps with more than one target such as Raptors.

His Q, Consume, still does true damage verses monsters, but he can also now use it against champions in which case it does magic damage.

His W, Biggest Snowball Ever!, boosts his movement speed by a lot and prevents him from being slowed. This thing has a ton of uses (use it to get out of base quickly as one example) and will likely be the ability that takes the longest time to master. If you hold W down it will create and snowball and Willump will push it along and it will grow in size up to a point (I'd say about a 1/3 of a lane or perhaps slightly wider. Using it is kind of like drifting using Sion's ultimate though I would argue that it is easier to steer than Sion. Tightening or widening the turn can influence your ability to control the snowball, which is where the skill expression will come in. You can also release it when you want to do things like zone one of the enemy team out of fight or force them to move it an advantageous direction for one of your teammates to follow up on.

His E, Snowball Barrage, has Nunu throwing 3 snowballs in the direction you point. You can reactive it up to three times, so it is fairly easy to target three nearby enemies with a different cast, but you can actually hit more targets than that if you hit them will maneuvering and re-casting the ability. Targets hit by it are damaged and slowed and at the end of the duration or three casts targets that are marked by the ability that are in range of Willump will be stunned.

His R, Absolute Zero is still pretty much the same. If you move or the channel gets interuppted you will only do a portion of the possible damage. The one big difference is that Nunu & Willump get a shield based on their bonus health that refreshes each second during the channeling of the ultimate, so if you've built a good chunk of health and pair it with Aftershock you get hella tanky.

Not going to lie, running around with the giant snowball and watching champions trying to scatter so as to not get stunned is pretty amusing.

Runes copied from Valkrin a challenger and sometimes jungler.

I meant to go Aftershock, so I may update this with some numbers from that keystone when I have a chance.