Guild Wars 2

Basic ui invisible but you can still open inventory, map, etc. I’ve already learned where my skills are and it would be nice to get immersed in the game, not the ui.
Could have a see through(but still visible) version of the health pool/party window so you can still heal/support at the right times. And/or have it like chat, only pops up when it changes.

Closest you can get is Ctrl-Shift-H

At this point in the life-cycle of the game the customization is rather low and limited.

I know, I like to play with ui off but I cannot use inventory or any of the other windows besides the map