I'll start by saying I'm a usability expert and that's a big part of what I do in my profession.  Basically, how do people interact with apps, games, and devices.

There are two pretty big issues I've found from a usability standpoint that I think detract from the game.

1. I can't understand a word that anyone is saying while someone is speaking to me while on a mission.  It's all garbled and impossible to understand.  I could read the text, but i'm not going to do that while fighting.  What usually ends up happening is I miss the story content.  Solution: Remove 90% of the sound effects on the audio file.  You can still keep some of the grittiness from the audio, but at least make it easy to understand.
2. The crafting interface is not intuitive at all.  I had to watch a video on the internet on how to use the advanced materials.  Solution:  Make the glow effect impossible to miss when selecting a component.

These are just my thoughts anyway.