When it comes to content, the new dungeons and new lair challenges will be at the top of the list. The new dungeons, Dreamscale Ruins -Hall of the Eclipse and Rutus Mines - Halls of the Dead, will be for level 40+ with gear score of 1516. The lair challenges have the same requirements, with some very powerful S+ armor obtainable if you win.
Armor drop rates will also get some tweaks, with S tier items dropping more often, twice as much, and with more variety as well. They'll also come with a new set of rules, as they'll be character bound when obtained, with storage limits. An unbinding item will be added sometime later, so choose which to equip wisely for now. You'll be able to also salvage these S items for materials for coming Runes Adjustment changes, so save them up if you get them.
The Warlords Arena will get a major change, with the whole thing going casual mode. This new mode means that all characters entering will play as if the same level and stats, but you'll be able to gear up as you'd like so the difference will come to gear and skill in the end.
There are some changes for combat and PvP as well. PvP Battlefield Season Radiant Sun also begins with the October 28th update, with rewards for weekly and seasonal challenges. Each class will also see some changes to its Blessings, mostly a series of stat changes to balance things out.
For the full update, including the armor types you can win, the list of changes to Blessings, and more, see the announcement here.