ZDoom acquired, thanks cheps, and I'm just now playing the original Doom to lube up before I let John Romero slide between my buttocks and make me his bitch with his newly minted masterpiece.
I'm still on the original first episode right now though, so here's a hilariously late and pointless rant about 1993 level design.
Doom E1M4
See picture here, with points of interest marked (A) and (B):
http://i.imgur.com/f1WCMeU.png
You find the yellow door, open it, and enter into the level exit room, but you soon find that the level exit is blocked because a small bridge needs raising (B) There is another door out of this room, and you go through it to find more gameplay, and loop back to the start of the level. You then proceed to spend the next 30 minutes wondering how the fuck you raise the bridge to the level exit, wandering all around the map over and over again and around in circles.
Turns out the switch to raise the bridge is that red thing (A) next to the yellow door just before you enter the level exit room and even notice there is a "puzzle" to solve.
Fucking lol.