What was good to hear so far is that no one has really stream anything of the campaign parts so far.
DLC related alone, the view is we'll be getting similar to Osiris DLC in regards to new story missions, new adventures and new quests. New place to explore (Ice caps on Mars) which is far bigger than Mercury.
I think the key to it this one being worthwhile is the new horde/patrol/wave mode called Escalation Protocol.
In direct comparison to Osiris, we had guns to grind for from existing content whereas this is a new mode entirely that will have a unique reward from each boss. Apparently, they had one final chance after the Summit to take on feedback from the youtube and twitch attendees and crank the difficulty up a notch.
I'll add other elements on different threads as not all relate to DLC.
Oh, almost forgot. 16 exotics come in with DLC. 8 new and 8 old, including the Sleeper Simulant. I'm really hoping for a secret quest to chase for that one. Not something that is just handed to you.