The Chaos Project (DOOM II WAD) - Gameplay (w/ commentary)
An 18-level episode created by Jonathan D. Campbell, made for the Boom source port, with mostly simple levels and basic level design. The story is yet another one of those taking place years after Doom and Doom 2, where there was a hidden project complex on Earth with great and deadly experiments, producing an optic gate that allowed travel between dimensions with power from a power plant. However, this brought Hell's attention again, and so the demons jumped through the gateway and took over the project complex and power plant, beginning another invasion of Earth. The marines were briefed on a mission command on the mission to destroy the source of the abomination. By the next day, the marines had all been slaughtered, except for one guy as he had been passed over. Once again on his own, the Doomguy went through the doomed city, retook the subterranean complex, went to the gate navigation facility to reach the drop point, and reached the power plant in attempt to shut it down, but the switch was broken and the demons are preventing the power from shutting down, so with the only choice being to let the hordes continue for the time being, the marine eventually went over to the project complex and reached the optic gate leading to Hell. He manages to drain the Godless Abominate of its blood and returns to mission command, but it's not yet over since the cyberdemon is lurking deep within the unseen parts of the facility, as the forces of Hell have fortified it a bit to their liking and must come across them once more to once again get out of mission command alive.
Sure, the level design isn't much here, but I still say it's an enjoyable megawad overall. So you can go play this if you have the chance. There's a 20th level in here that I have heard of but I'm not sure if there's a way to reach it from the "QUIT NOW" levels besides warping, so I didn't get to it in this video as I assumed it was the end already.