What about Legion would you change in order to "fix" it in your eyes? And, if you could, go into detail about that change.
For example, I would definitely redesign the legendary system. No one likes the RNG, I would make it so that each legendary you got FELT legendary, and not everyone had two.
An idea I had was make getting a legendary (still have a few legendaries per class, but you can only target one), a longer process a la MoP or WoD. Perhaps you had to work with Odyn or Kalecgos, and make it similar to the Balance of Power questline where instead of forging more Power for your artifact you created a legendary. Something that gets rid of the asinine RNG
Another change I would make is to the artifacts. Instead of grinding out every single trait, make the Artifact Traits similar to talent trees, where you can only take certain paths, but can refund and change them just like talents. That way, you can create different builds, and have almost "sub-classes" through the artifact. Artifact Power could still function similarly, but this way every trait isn't needed, and increases ways to customize your build.
How else would you change Legion?
inb4 "Change everything!" Not an argument