Diablo III. Chiefly, the patch is intended to lessen the gaps between solo and co-op, single-handed and dual wielding combat, and monster buffing.
In a bid to make co-op more attractive, some of fixes will remove key mechanics. The first change will be removing averaging in multiplayer games of Magic Find and Gold Find, much like 1.03 removed monster damage increase in co-op. In addition, the patch will lower the health multiplier for monsters per additional player in co-op games as well.
Also, Blizzard increasing the health of normal monsters by approximately 5%-10% in Inferno, but also increasing the likelihood they drop magic or rare items by a factor of four. At the same time, the developer is lowering the health of Champions and Rares by 10-25% and editing specific affixes to shrink the difficulty gap.
Weapon damage is another area that the developer is closing the gap on. The raw damage value on all level 61 and 62 weapons will be able to roll damage that extends all the way to the top end of level 63, while improving two-handed melee weapons by creating a new set of stronger affixes to compensate for the loss of stats that can come from the offhand weapon.
Blizzard is also removing Enrage Timers and the “heal back to full” behavior from Champion and Rare monster packs.
Post-patch, the developer is also improving Legendary items. The developer will release patch notes on them as they are implemented.