Resist & Death
A Scar from a God
At the end of Act 5, you might have noticed a line in your chat pane about "being weakened by Kitava's cruel afflication". This is the story justification for the introduction of lowered base Resistances and a Death Penalty, which used to happen as you entered the now-removed higher difficulty settings of Path of Exile (the former higher difficulty settings were rolled into Acts 6-10).
Your resistances now start at -30%, meaning you take extra damage from Fire, Cold, Lightning, and Chaos damage sources. You now need 105% total Resistances on your gear to hit the 75% cap, something you should absolutely seek out gear to do ASAP. In particular, try to cap Fire and Cold resistances (the main sources in Act 6). At the end of the story, you'll take a similar penalty of another 30%, which sets your initial resistances to a total of -60% before gear.
In addition, dying is no longer effectively free. Deaths from now on will cost you 5% of the maximum experience required for the next level (1 "bar" of experience) each time. This, too, rises in the endgame to 10% (2 "bars") of experience lost after the completion of the main story. Gems do not lose experience when you do, and you cannot lose a level by dying (only be set to the minimum for your current level).