D3:
there were 3 alternate treasure golem skins that only were a slight color variation. They were removed and replaced with 3 new total redos. Theses 3 new ones each drop different treasures, one drops only gems, other does plans and craft mats, third does blood shards. treasure golems will also appear on minimap now.
2 new legendary gems.
a lot o the original areas having tileset redone so when doing rifts you'll get a random map for the same area vice the same one over and over.
buffing the lesser used pylons and making sure a certain minimum will be in each rift.
retuning the rift guardians.
retuning the random dungeon generator for more interesting and evened maps.
reducing death penalty when you did far away from checkpoint by adding a rez at body with timer similar to wow rez timer.
revising achievements/conquest from seasons. and some looking pretty hard.
getting to 70 in season will unlock 2 pieces of transmog for a season transmog armor set.
showed off some of the new season legendaries.
adding ancient items which are legendaries with additional stat weights.
new mobs, rat king and yetis.
tristam layout changed so all vendors in close proximity in first open area.
new area, the now empty barbarian city on mount arreat that was wiped out in D2.
at end of season, all gold and paragon xp will be automatically added to your non-season chars, items in stash will be mailed to you.