10.2.0 brings bug fixes and performance updates, as well as new content. One, like many already know is the NEW 5-Star Hero: Vile Songstress. She will be available in the mines. However, she will replace Spirit Arbiter in the Ore Mall, so if you haven't finished farming Spirit Arbiter shards, you'd better hurry.
There are also new creatures added from the update. All are 5-Star creatures though. The first one that's made available is Belphegor, but she is only awarded as a top-tier prize for the 4th and 5th place Merit Ranks. There are 3 others, (Aries, Hera, and Ordinance), but they aren't available yet.
There are various bug fixes such as the Grandmaster Cup bug fixes, and Lucidity will no longer trigger if the hero's rage is below 80. There are many others, but, you can just check out the details here: http://dh.forum.igg.com/topic?fcid=1&ctid=7864