This game has some really peculiar design failings.
Believe it or not, I'm fine with their post game structure. The gunplay is fine. The small explorable (super linear) maps are fine. The barebones loot/RPG system is acceptable.
I could live with ALL of these things and enjoy this game casually for quite a while despite the low end cap if they fixed one major thing:
Communication.
This is the kind of game where, ideally, you approach it Phantasy Star Online style and run around the hub city looking or people to party up with via chat. You find people. Socialize. Group up. Go hunting.
or.
You're solo grinding through the missions and you happen upon strangers. Help them. Communicate via proximity-based chat. Either Join their fire team (to talk to the full group in a party chat system no matter where they are, and share exp), or continue on your own questing and helping/chatting with randoms as you drift throughout the world.
I didn't buy this game for the PvP, although I'm glad that it's there should I want a change a pace. I bought Destiny because the MMO-lite mechanics with a Halo feel. That's what was hyped, and that's where this game drops the ball in a serious way.
The art, style, gunplay, enemy diversity, mood - all of that is fine. Unfortunately, I'm already bored at lvl 5 because the game experience feels so isolated and silent.
I just did a mission where many of us where in the cosmodrome of Old Russia. You're fighting waves of enemies and eventually the big spider-boss. NOBODY can talk. There were plenty of times we WISHED we could, like when I ventured off into some catacombs alone to face down an angry wizard. OR when we finished against a wave of guys, and some of are just staring at each other wondering what mission the person is on or if we felt like doing something else in the map. Why would I join this person's fire team? I don't know him. Why can't we just proximity chat to shoot the breeze, share tactics, or just say, "hey man, you feel like doing some Crucible?"
This isn't a Single player game. The story is barebones. The game pretty heavy-handed tonally, and neither the maps nor the way that missions are doled out are designed in a way that is deliberate for solo play. It's not building on the SP game with linear set pieces, COD-style either. It's an small MMO-designed game without the MMO mechanics of communication which is KILLING this game for me.
Fixing this major element changes the entire game.
With this in mind, you can enter the small hubs, play and explore casually in a connected space communicating with people even as a soloist. Bungie can add more boss encounters, change up the maps, change out the loot - basically treat it like the Adventure Mode of Diablo 3: Ultimate Evil Edition - and the game would be great with long legs.
As is, it's a mediocre SP game, a troubled MP game, and disappointing because there's so much that is great about it. It's a gorgeous game with Bungie's excellent shooter mechanics behind it.
This game doesn't need a Destiny 2 to fix the problems. It simply needs to fix some core aspects of it's MMO concept - mostly the joy of talking and exploring with new people - and Bungie would have a very different reception. Let Destiny 2 worry about the other stuff like improving this ridiculous story, making better loot and bosses, and expanding the game world.
As is, Destiny is so close that it's annoying.