Maybe you saw this coming as soon as it was announced that Destiny 2 would be coming to PC - dataminers have cracked open the Destiny 2 beta and found a ton of info about the upcoming game, including some SERIOUS STORY SPOILERS. If you want to go into Bungie's sequel completely fresh, proceed no further. Seriously, turn back now. Consider everything after this paragraph to be a Darkness Zone, no respawning allowed.
You sure? Okay then.
Who else survived the Tower's destruction?
Not just the most important and beloved characters survived the fall of the Tower. Each of the faction leaders, Banshee the Gunsmith, and Master Rahool the Cryptarch also made it out. It's not clear what role they have to play in the events of Destiny 2, but if I had to guess I'd wager they'll take up their old roles; sending you on Patrol missions, selling you weapons and ammo, and ripping you off, respectively.
Ghaul is not the only bad guy
Destiny 2's big bad is as imposing as they come, but it would be silly to think he and his Red Legion are the only villains standing in our way. Before we get to Ghaul, we'll have to go through one of his lieutenants, Thumos.
There's also the matter of the Taken King, Oryx. While his presence isn't confirmed, one NPC ponders aloud, "What if Oryx isn't dead?" He was a pretty popular villain in the expansion which was named after him , so I could see Bungie bringing him back.
Lastly, the Fallen have already shown themselves to be one of the more diverse factions, with multiple leaders and philosophies. Some of these clans are already allied with us, but one NPC wonders about furthering that relationship in order to drive out the Hive hiding in Saturn's moon, Titan. Oh those Hive, they sure do love moons.
Not everyone makes it out unscathed
At some point in the story, Cayde-6 gets his arm shot off. No word yet on who does the deed, but he's a robot so I'm fairly sure he can just get a new one and will be fine. Please be fine, Cayde.
How it all ends
No big surprise here: Ghaul is killed at the end of the campaign. You didn't think he was gonna back down or run off with his tail tucked between his legs, did you? Nope. In the wake of his defeat, it sounds like we'll either retake the original Tower or build a new one, though that's largely conjecture.
The really big shocker is with regards to the Traveller. At the end of the game, it wakes up, and a new Golden Age begins. As far as endings go, I think this is right up there with "Master Chief, you mind telling me what you're doing on that ship?" "Sir, finishing this fight" in terms of cliffhanger-ness.
The first DLC is The Curse of Osiris
If you were one of the best of the best in the original Destiny PvP, you might've had a chance to participate in Trials of Osiris. According to Kotaku, the first piece of Destiny 2 DLC will be all about this enigmatic space wizard, and will add a new Patrol zone and new social space. The story (because remember, Destiny has a story now) will be about rescuing Osiris from the Vex.
Look, I'll be honest here: cool new features aside, I just want that cool-as-hell Anubis armor from the original Trials.
What about the Raid?
The only audio file that seems to refer to the Raid so far is someone asking if it's true we flew into the Sun. A PlayStation Trophy refers to the Raid as being called "Leviathan," which points us to a few other clues. There are several creatures and references in the Destiny Grimoire which could be described as leviathan at least in size if nothing else, but it would seem that this one is a Cabal-made super-weapon that eats planetoids. Here's some concept art that shows its enormous, gaping maw:
Meanwhile, fast-forward to 3:35 in this making-of video and you can see three Guardians staring past debris into a glowing orange light with Vex architecture behind them. Other than the number of Guardians being too few for a Raid, that seems to line up pretty well with what we see above. There's also this infographic further supporting the theory.
As for who's steering that thing, why it exists, and just how big it really is, nobody can say for certain yet. Raids have always unlocked a short time after launch, so I imagine it won't be long before we have some more concrete answers. And besides, reading about this stuff is nowhere near as fun as playing it.