Apparently there is a huge phenomenon with them that shot off again the last few years or so, to my amazement some dude actually developed an ASCII version of DooM and it is still up for grabs. I am surprised anyone actually updates these particular RPG's every now and then. What does scare me about the DooMRL site though is that they offer unstable builds of the source code and something else I am too lazy to check up on.
Speaking of DooM Rougelike, I've played it myself and it is rather challenging at random. Do not worry though, the enemy types are represented by a letter!