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, particularly for 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).