There are really two games here. #1: "Survive to level 20" is challenging, #2: "everything else" is super easy.
So the big tip is that at character creation and early level ups you need to focus on survival. Werewolf (fast health regen), Celestial (healing), many points into Stamina are all good ideas for the first 20 levels. Ice resistance near 100% is also important starting in the late teens.
After L20, you will level up much faster than the mobs so raise stamina/willpower to comfortable levels and then pursue whatever damage-dealing strategy you like. Critical Strike + strength is pretty hard to beat, by L85 or so you'll 1-hit everything with >10K damage.
Easy, and pretty repetitive. 3/5.
Teleport is your friend for Level 10 - I had about 15 L5 teleport towers by the end, which sufficed to not leak any creeps in levels 65-75.
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