Aiming and interacting is locked to the HUD centre point, so it's a bit of a nightmare unless you're really good at keeping your head completely still and pointed at the middle of the screen (unfortunately I'm not an owl

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I wouldn't be too bothered if the main UI windows stayed in the "always forward" position, even though that would be a bit weird as your don't turn your head inside a remlok helmet like in a NASA space suit: The helmet faceplate moves with your head.
Really though, it should be a choice to have the UI windows locked facing forward or following head-look, so that everyone gets to choose their preference; Motion sickness and disorientation considerations need to be made as not everyone reacts the same to 6-degrees of motion.
However, not having the "cyan dot" HUD centre follow head-look, and the item and NPC label icons drifting as soon as you look off-centre really needs to be fixed to make it playable. At the moment in order to aim, interact and read labels without needing supernatural neck muscles its easier (at least for an old codger like me) to disable head tracking completely... which is a shame as other than the UI it's the best first person head tracking & movement control implementation I've played.