Destiny has had a rocky road, to say the least. Despite a strong launch back in 2014, the game was immediately subject to criticism over many design and gameplay choices in the game. Now, with Destiny 2 on the way, Bungie has to be focused on not repeating the mistakes of the first.
An Actual Story
The biggest criticism of the first game was the lack of any real story. One of the selling points leading up to Destiny's release was the idea of a cinematic story that would take players across the Milky Way, defending the Last City on Earth from aliens seeking out destruction.
When the game was released, the promised story just wasn't there. All it did was send players place to place to shoot aliens because they're the bad guys. Bungie rebounded a bit with the releases of The Taken King and Rise of Iron expansions, which added some actual story and lore, but never got all the way back from the empty "story" of year 1 Destiny.
This looks to be the biggest thing that Bungie is addressing. Since Destiny 2 was announced, the constant message Bungie has put out is that the cinematic story promised in the first game will be there. The debut trailer promised an epic war with the Cabal, so hopefully, it will deliver.
A Living, Breathing World
Another issue from the first game was the somewhat empty maps players explored. While the vistas were beautiful to look at, they always felt empty, with random enemies dotting the world at the most. There was never any incentive to go back to explore the worlds to see if there was some hidden story you could find about the history of this universe, or visit characters that spent time in the worlds because they weren't there.
This may already be addressed by Bungie as well. Again, to go back to the debut trailer, it focuses on the destruction of the Last City. This sort of event would force its inhabitants to go out into the wilds of Earth and maybe the other planets in the solar system as well.
This could mean that towns, villages, outposts, etc. may actually fill out the maps, encouraging players to explore each world to see where everyone ends up after the attack and how they are dealing with it. It would give the world a life that, as mentioned, just wasn't there in the first game.
Unique Gear
A big reason people stick with Destiny, despite the complaints, is the loot. This is a game driven by the desire for bigger and better gear. Unfortunately, after a while, the first game just ended up recycling the same weapons and armor, with the only "variety" coming in the form of stat changes and maybe a different perk. After a while, everything just started feeling like a reskin of something else. Granted, the aesthetic differences were cool, but those, as time went on, started losing their appeal.
Bungie, again, experimented with this in the first Destiny with the introduction of weapon foundries, each of which had a unique aesthetic along with perk trees to match. But there were only ever three, with other foundries teased by the exotic gear, but that meant only one or two items were from that foundry. If Bungie goes deeper with this and provides a unique separation between gear based on activities and factions, it would keep the loot drive up and keep players striving for better gear.
More Colorful Characters
Building off of the story angle, another issue in Destiny was how undefined a lot of the characters were. When the game launched, they were all talking heads there to provide missions or rewards during the course of the game.
As time went on, some did get a little more defined, such as Cayde-6 coming across as the smart-mouth member of the Vanguard. But even with the number of characters shown and teased, it still left a void in terms of meaningful interactions.
With the city destroyed, this could give players a chance to see what a lot of these characters are like away from the social spaces. Zavala is meant to be this stoic character and natural leader, he should be shown rallying guardians to fight back outside of just the trailer.
On top of that, bringing teased characters into the actual world could also aid in growing the story and lore. There are characters, like Toland the Shattered or Osiris the Exiled, that could make the game even more interesting and open up a rabbit hole of lore for the player to jump in.
Match-make Everything
Stepping outside of just making a bigger universe, matchmaking and LFG have been a consistent problem. Destiny is designed and intended as a shared world experience, where players join up and battle these aliens or each other all over the Milky Way.
After release, though, matchmaking proved to be quite limited in terms of what was available. While it makes sense for something like a raid to not have matchmaking, given the difficulty and cooperation needed, the lack of any Looking For Game feature in the game itself didn't help.
Adding this in would help solve a lot of issues for a lot of players. Destiny prompted a wave of third-party LFG sites to make finding groups for raiding and other activities easier. That gives Bungie two options for Destiny: add matchmaking to all modes or have a built-in LFG feature.
While adding matchmaking to all modes removes every headache, the players asking for it could regret it when they start getting thrown into matches that could only aggravate them. That is why a built-in LFG system could be the best fix. It would keep everything in-game, but allow players to have a level of control over what they are doing.