Ultra Doom2X (DOOM II WAD) - Full Singleplayer Playthrough (w/ commentary)
This is a Doom II wad created by Chuck Lai which is mainly a weapon and enemy enhancement mod with a storyline that takes place after the events of the base game, although the levels are mostly the same as the original with several tweaks. The original version was known as "Doom2X", but Ultra Doom2X is an upgraded version of the addon with bugfixes, as well as a newly-made map for MAP32. Ultra Doom2X was first released on the PC Gamer September 1996 issue (which also notably contained the shareware release of Quake, id Software's next game). While Chuck said on https://web.archive.org/web/20100621063651/http://www.parkerinfo.com/dmdo/index26.htm that the original Doom2X was on that issue, I was only able to find Ultra Doom2X there, so it seems as if the original had actually never been released.