My loyal Galaxy S4 alerted me to this article as the phone is aware of my obsession with Destiny. The article talks a bit of the new PvP maps, the new story missions, Crota's End loot drop system, and most importantly, the upgrade mechanics of taking current exotic gear and bringing it up to the next level of damage/defense for weapons and armor.
http://www.gameinformer.com/b/features/archive/2014/12/03/7158659.aspx?PostPageIndex=3
*Contains, spoilers/descriptions of activities in the new story missions, but not the raid.
If you want to upgrade exotics, you'll be able to do so on the weekends with Xur, but can only upgrade specific items. It'll cost somewhere around 7,000 glimmer, probably give or take 1,000, an exotic shard, and the exotic item. When doing so, all upgrade progress on the exotic will be reset and need to be releveled. Upgrading the new version may be slightly faster than the first time.
http://www.bungie.net/7_The-Dark-Below-Preview/en/News/News?aid=12442
Shows examples of what the new Xur selection will look likes. Also has a lot of the game informer article summarized as bullet points.