Grinding Gear Games have posted a lengthy summary of balance changes that will arrive with the Delve update on 31 August 2018. In true Path of Exile fashion, there are more balance changes in there than most games get during a whole year.
If you single out one balance change that got fans hyped up, it would be the way spell blocking works. There will no longer be attack block abilities that shift into spell block, and they will now just be spell block. This change will allow players to have reliable spell block tools on any character, as opposed to just being overpowered on high block characters and weak on characters that didn't invest in blocking.
On the other side of the spectrum, traps are getting nerfed. Apparently they were so powerful that they "invalidated other ways of using many skills". Throw time on traps has been increased as well as damage penalties for Multi Trap Support and Minefield Support. Tap and mine skills will also get higher damage to compensate for some of the power loss.
Instant skills will also function somewhat differently now. They will not longer require other skills to finish casting, as they can now be used in conjunction. That said, the instant skills will not be usable while the character is disabled via stuns or freezes.
Apparently, a large number of effects are now instant, most of which are buffs. Other than that, most of the abilities such as Molten Shell, Phase Run, Blood Rage, Convocation and Righteous fire were otherwise left untouched. Considering the listed changes are too big to simply list out here, you can read up the entire post on the official forums.
Grinding Gear Games
Make sure to also check out the challenge rewards that will be coming with Azurite Mines, as you plan on adjusting your character to get the most out of these new changes. It will be necessary, as the mines will put everyone's ability to test, since the dungeon is endless and only becomes harder as you progress.