image retention?
The studio is reading this thread, so they can discuss your thoughts about a hardcore mode and HUD opacity. Do note, we did hire a dedicated UI/UX several months ago and work on that is still constantly happening and evolving.
He speaks about image burn-in which is something you need to worry about on Plasma TVs, and even sometimes on LCDs. I'd say make sure to fade out the HUD completely when there's no action going around and everything should be good. Kind of like what you have in Uncharted, I think. *edit* OK I see you already answered this.
Your UX designer is probably coming from the place where usability takes precedence over any kind of experience, but IMO, games are much more about experience than something like website. You don't
really need to know what your health is while you're just walking around, and your health doesn't really need to be toxic bright green so that you can't miss it on the screen. Especially not in single player potion of the game, I'd say.
Then there's also the legitimacy of the look of the UI. What I mean is, despite how functional and clear UI is, you don't want something that's using sci-fi fonts and gauges in a medieval themed game, because it takes you out of experience too much. Your UI looks highly neutral/clinical, I'd say, it's the kind of look that exists on it's own and is not partial to any particular style of the game. It would work in a sci fi game, but also in a game like this. I know some people wanted to see a more dilapidated UI to match the dilapidated look of the game, but in my opinion, your game does take place in the future, so no matter how ruined it is, it makes sense to have a UI like this, which would probably be something familiar to people who live in that world from whatever remaining technology they have (or memories of it). If this is the reasoning behind the neutral/clinical look, I think it's fine, even though it probably wouldn't be my first instinct to go with it.
If there's any takeway advice from all of this, it would be to not use toxic green health bar (it's really kind of distracting) and to make the HUD fade when not needed.
Listen mode is mapped to a button. Don't use it if you hate it, but it's not a massive advantage. You can't see things from across the map, only if they are making some sound, slows you down, etc. It will be a give and take. But if you hate it, and you want to be all hardcore, don't hit the button. You do have some self control right?
This is fine, but then you have to make sure that the game is possible to play (without cheap deaths) for people who decide to not use it. If the game is "normal" difficulty when using it, but "hard" when not using it, that's fine. If you have to die to see that a group of enemies is in some room, then it's not good. You can peek behind the corners here just by rotating the camera, right? I see people suggesting to add a peek behind action, but if I remember correctly, a camera rotation would be enough.