Kaldheim is a realm of, gods, monsters, and Norse-inspired elements. There is adventure, but It's not an adventure set in the same way that Zendikar is. Here, people want to do epic feats in battle so they can be remembered in sagas told by their clans. While there are gods and heroes, as in Theros, it's a very different tone here. You're more likely to have a beer with a god on Kaldheim than worship them. Gods are more powerful than humans, but they are mortal here.
Set Boosters are a new kind of boosters first introduced in Zendikar Rising. If you intend to purchase packs to play with, then the Draft Booster is your best option, but if you want packs purely for the joy of opening new cards, then the Set Booster is for you!