A bad part about 100%ing the world was GW2 making me explore each of the Copy-Pasted Borderlands 3 times total where the vistas and POIs are exactly the same. Another bad part had to do with buggy map features, like Straits of Devastation's southwest skill point that required me to camp the challenge during a nightly 3am reset.
But I love vistas and conquering the puzzle and path it takes to find them - in fact, I was actively disappointed by vistas that were basically in front of me without any special or difficult path to get to them. A couple of the vistas in Dredgehaunt Cliffs were especially brutal and incredibly fun to finally achieve.
I like vistas, but I'm not a fan of platformer games in general (I don't really even like Mario games anymore), so the fact that I like vistas at all is saying a lot.
Again, I wish I liked 100%ing things in games, but it's usually torture and sucks all the fun out of the game. Anything that involves doing absolutely everything devolves into a mechanical affair, which automatically turns it from a game into a job. It's not the game's fault. That's a flaw with video games as a medium. I suppose some people enjoy doing absolutely everything, but I liken 100%ing things to doing my taxes.
What I love about games is that emotional engagement. That "wow" moment, and the way the game tries to connect with you in unexpected and exciting ways. What I don't like about games is performing repetitive or time consuming actions for an eventual reward. At that point, I can't help but ask for a steady salary for doing so.
(running dungeons for gear is just something I will have to live with. At least that's mostly bashing things in the face, rather running long distances to do something largely uneventful)
I think what keeps me interested in dungeons is the teamwork, the interesting encounters, and in the case of GW2, the really cool set pieces and tools you're given for a specific encounter.
Arah is my favorite Light, CoF is pretty nice too but I'm sure it's level 75.
All exotics after CM are 80, so you actually get a pretty wide selection of dungeon gear to choose from.