Here's my take on the exit door.
The exit door in the orginal doom is one of those hallmark designs that, bar that you've played doom ofcourse, you'll recognize anywhere.
It has a distinct H.R Giger'ish feel to it.
It, quite rightly so i suppose, stands out from everything else pretty much in the entire game.
This was sort of in doom 3 changed to an elevator or the airlock (which granted was quite cool actually :)).
I've tried to hit something in-between'ish and like with the rest of the door designs it had to fit an overall style (where the round iconic cables didn't really fit well with) - i've tried to remedy the missing cables with a strict set of tubes...i think i'll try and hint at it being an exit without resorting to a sign as in the below screenshot :P.