I spend a lot of time thinking about what does and doesn't work in destiny, and what I would like to see in future destiny games or my own theoretical "perfect" game using what I enjoy in destiny.
So far, I've noticed a pattern: my favorite encounters in Destiny are the Oracles in the VoG, the Stills in CE, and the Siege Engine of WotM. Obviously, the common thread to all of these is that they reject the classic "Boss" in favor of a simple objective in a challenging arena.
It's in these moments that the players become something more than "bodies on plates" as happened a lot in King's Fall; there is no "programmed", correct solution to these encounters. There is only what works to get you and your team through.
It tests your ability to think on the spot, to judge, "Can I rush this enemy, or do I run and risk it attacking me or my allies?", to ask yourself and your team, "Can we 5-man this? If someone else died, could we do it with 4, or 3?" It gives you the opportunity to go above and beyond, to really strut your stuff if you're a good player. Additionally, since the arena no longer centers on a single entity, the area opens up and players can make the fullest use of the mobility that's unique to Destiny.
Contrast this to the more mechanical boss fights such as those in King's Fall, where one's contribution to the team can never be more than a successful completion of your assigned role. While this does mean that people can't be carried through a raid, it ultimately felt bad for all involved. It was stale and unrewarding for the "carriers" who were now limited by the weakest party member, and the weaker party members now had to suffer hours of wipes. Not to mention, when each boss fight is just a repeated ritual, movement becomes static. You stand in place a, perform your function, move to position b, perform that function, then follow route c back to a. There's none of the freedom that sets Destiny's gunplay apart from every other shooter out there.
It feels to me, like a big part of that restriction is rooted in a mental fixation on the players fighting "classical" bosses; if the main event is to kill a giant bullet-sponge, then the best you can do as Bungie is to try and build all these encounters around making them vulnerable. It works, but it gets repetitive when every fight is organized into Ritual -> DPS -> Repeat. With encounters centering around repeated rituals, there's only so much strategy the players can employ before they break down into the machine-like repetition of a process, which isn't nearly as fun as the wild, off-the-wall, win-by-the-seat-of-your-pants action that comes of non-boss encounters.
Personally, I'm hoping Destiny 2 and beyond pick up on this, and focus more on "arena" encounters rather than "boss" ones, and I'd be psyched to find a game that takes this idea to its fullest extent.