It literally does start where Doom II ends, cool! 🤓

Also, it looks like an early preview of the mod's graphical features

Gameplay Playlist
https://www.youtube.com/playlist?list=PLH9X4m3s2fcdjQApDi1de9AGhjtwVTPA8

About the mod

Doom III is a Mod for the 1994 hit Doom II by id Software. This mod let's you get back into the fight against evil and it's gameplay is modernized while still playing very much the way Doom and Doom II did.

Fight your way through 2 Chapters of new levels, SinglePlayer or Coop. Play as Doom Guy, Doom Gal, or one of the other selectable characters. Customize your difficulty by chosing your Character, Skill and Save-Point amount. Alongside all the well known monsters, items, weapons and power-ups there are also lots of new ones, to help you fight back the demons.

Get the mod
https://www.moddb.com/mods/doom-3-doom-ii-mod
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https://www.youtube.com/watch?v=EoqpSGoCXEY