honestly, I think the one thing they clearly got wrong was just too much mist.

If you look at the trailers for ML you realize that they dramatically toned down the mist for those and it actually looks good, which makes sense. If they tried to promote the biome by showing it the way players actually experience it, it would be like... uh, I dont see anything (I wonder what that blue light off in the distance is).
Yes, even with extensive wisp lights, you just dont get the kind of dramatic views and vistas that are shown except during the brief times when the mist temporarily recedes. So they clearly appreciated the need to tone down the mist to promote it, just not to play in it.

It's just so claustrophobic that you never really get a sense of the grandeur of the place for most of the time you are in it, and so even if you did have more open area to work with, it would still feel closed and uninviting.

They were clearly trying for something similar to storms in the mountains, or the fog in the plains, which are the other cases of the environment introducing limited visibility and adding extra hazard, as well as giving it a defining atmosphere. The difference is that those are more exception than rule, and atmosphere is fine until it interferes with enjoyment. They just need to tone it down (a lot).

I love the feather cape. Magic was also done well. I enjoy the chickens. The new armor is just better armor, so nothing really remarkable. And the new weapons are nice, but not really game changing.