One of the greatest concepts in
PoE goods is its own passive tree and ability gems. Each time you level up, you unlock points that you may use to uncover nodes in the passive skill tree. Minor nodes provide slight updates to your stats, while important nodes unlock powerful passive skills that fundamentally change how you perform.
This works in concert with ability gems, which slot to parts of gear and give your character charms and abilities to use in combat (unlike Diablo 3, they do not have any given abilities). Items will often have numerous gem slots, and at times they're linked together. If I set an ability like Orb of Storms into a slot and then join it using Curse on Hit, Flammability and Vulnerability, each time that my Orb of Storms hits an enemy it will also use both of these curses to them. It is basically an extremely robust spell-crafting system.
But it's when ability gems and the tree overlap that things get very exciting. My Necromancer relies solely on Scorching Ray to deal with damage. Naturally, I've unlocked lots of nodes which boost fire damage, but a few big nodes possess these clever synergies that are really enjoyable to unlock. Take Elemental Equilibrium for example, which makes enemies I hit with
poe buy currency elemental damage temporarily receive 25 percent immunity to those elements and -50 percent immunity to other components.