A lot of combat related balance changes are coming with this update:
TL;DR = Difficulty is much less effective HP, some more accuracy and damage
Reduced monster HP scaling (new effective scaling is about half as strong as previously), new formula = base * ((1 + 0.1) ^ diff + 0.25 * diff)
Monster prot/res now scales at +1% per diff, which is basically nothing
Monster attack mastery now scales ~3x faster than other monster masteries (3.33% of monster attack additionally gets added as attack mastery)
Monster damage masteries (str/magic/range) now scale 2x faster than other monster masteries (2% of monster skills turn into masteries, i.e. at diff 5 a strength 100 enemy now has strength 100 + strength mastery 10)
Monster damage from gear (str/dex/int) now scales 2x faster than before (+20% per diff)
Monster agility now scales 1.5x faster than other monster defensives (better make acc scrolls!)
Each level of difficulty gives a 1% chance to double loot and a 0.1% chance to triple loot
Enrage timer is reduced by 7.5 seconds per difficulty, capped to 60 seconds as minimum enrage timer