For anyone looking use GZDoom but wanting to old-school look and feel with the low-detail graphics mode, you're in luck since the community has created a nifty little PWAD called RetroShader, which lets you play the classic Doom games as if they were played in a lower resolution mode without actually having to lowering the display resolution on the source port itself. The link below contains the latest version updated to work with GZDoom v3.2.0. and QZDoom v2.0.1., older builds of these ports will not work. Simply run this with your game (drag-and-drop, autorun it through config.ini, load through command line parameter, etc.) and behold G/QZDoom in all of its vintage glory. The original link to the mod by torridgristle can be found
here; download the updated version by Rachel Alexanderson in Page 2.
Speaking of GZDoom, this is a really late news and all but some of the ZDoom and variants' are now finally hosted in a single website by the dev team under the newly redesigned
ZDoom website where you can find the latest news and updates of ZDoom or similar ports, as well as the latest official downloads to ZDoom (discontinued), GZDoom (active), and QZDoom (experimental).
Another thing I forgot to mention about WadSmoosh is that it only works on GZDoom (or QZDoom); it does not support old ZDoom.