Looking back to John Romero's developments from ID software and later (Quake's engines, Doom's engines, etc) I found that two of Eidos developments at the time of DC release very interesting, maybe you already know, Deus Ex (1999) and Thief: the dark project/Thief Gold (1998) which uses Dark engine later released for Xbox, this last one has had good fan made improvements in compatibility these years...
https://www.pcgamingwiki.com/wiki/Thief ... rk_Project
Thief (1998)