the in-game experience

Deus Ex uses a classic format for a first-person shooter. Others such as Doom had a similar layout. In addition to floating (not being right against the edge of the screen), DX also allowed the player to adjust the color and transparency of the elements.  For a FPS, the player needs nothing to distract his attention from where the action is, so things at the edges of the screen are more for peripheral movement and navigation.  Too much clutter and a player could be flanked, or not be able to locate cover or an escape route.