One of the things that I personally enjoyed as a new player was discovering which skills had synergy. I discovered how well Fireball and Time Shift was when I was soloing Kraken and was under leveled, so I believe difficult content can really be a good playground for experimenting. New players should start off with some free respecs to give them room to experiment with skills and get comfortable.
I also really enjoyed the quest to enter Shuyal by obtaining Gleipnir.
Bookmarks