Hearthpwn

Voyage to the Sunken City pushes Multicaster Shaman, an archetype which revolves around casting Fire, Frost, and Nature spells. It also has a decent way to close out games with Bioluminescence on a wide board and a bunch of face spells. Then there's Piranha Shaman, which... exists, I guess. It's the first set of this year, so it's a good choice nonetheless.

Fractured in Alterac Valley is an amazing set for Shamans, both the Legendaries are good and there's a number of good-great Shaman cards there. Though it's only pushing one archetype: Freeze Shaman, and the returning player deck for Shaman gets basically everything of importance from this set, so if your friend got that, buying packs here won't give them much.

United in Stormwind is most notable for the Shaman Quest Command the Elements. It's not its time to shine, sadly, because Overload cards kinda suck right now, but you can try it if you want. Other than that, there's a Battlecry package which is really good and probably the real reason to look at this set, as Bolner Hammerbeak and Brilliant Macaw are amazing.

Forged in the Barrens' most useful addition for Shamans isn't even a Shaman card; it's Mutanus the Devourer, a card which synergizes amazingly with the Battlecry package from Stormwind, That's not to say the Shaman cards suck, but Elementals are kinda meh right now and the Murlocs are pretty bad.