The Frosted Hills was always my favorite area in Torchlight II, offering various things to do like vanquishing Nether spawn, or taking out a not-so-petty camp of bandits.
I'll be honest, I'm usually impartial to snow levels because, if done incorrectly, they can turn out monstrously wrong--and have, on many occasions. But there's something about this level in Torchlight 2 that makes it stand out above all the rest. Granted, I haven't played through the fourth and final act, yet, but I heard it was short and probably doesn't contain anything more grand than the Frosted Hills.
These hills are memorable for being the point where your character passes the threshold of slick beginner and enters into the ranks of 'getting somewhere'.
This is likely the point of the game where the difficulty curve rises the most steeply, and really makes you rethink some of your original battle tactics, especially when playing on one of the higher difficulty levels.