This isn't ZDoom. This is actually created from Doom Legacy: http://doomlegacy.sourceforge.net/I'm new here, but I've got some skills with Doom myself. I'm not sure what Doom engine you're using, but I can tell that in Z/GZdoom (Doom in Hexen) you have a linedef 181 to slope floors and ceilings to the nearest sector. Can be useful for creating loops. You have support for floor shadows, dynamic lights etc etc. Sorry if this is unneeded info, but what can I do as a new person? :D Cool game btw.
It is a very dated engine but considering the age of the project it's just not worth it to switch to a more modern engine because of the effort in porting all the material over. It doesn't support skyboxes, slopes, and many of the features ZDoom has, but it does make doing 3D blocks very easy.