Consider that "Quake," a game which came after Duke and was considered to be the primary competitor to Duke at that time, did away with manual interactions altogether. You progressed through the game largely via frottage; you simply rubbed yourself against walls and doors until they gave way, either by a scripted trigger or simply through vigorous abrasion. Duke could have been made as a response to Quake, even though it came out before: it had world as tangible, or more tangible, than many shooters today.
Things get more complicated when you start thinking about QuakeC, or native IP support, and then all bets are truly off the first time you entered +mlook at the console. I mean, that's when you knew. But as a design - as a place? For all its interdimensional chaos, you could eat off of Quake. Every molecule was clean. Duke, on the other hand, was filthy with ambiguities.
Jetpacks. Tricksy holograms. Shrink-rays. I mean, there are entire games based on individual Duke features. Timed detonators! It's like they had access to a different alphabet, and somewhere they are still hoarding those secret letters. Why are all of those ideas in the same game? It's from 1996, and it still comes up in conversation. The Subway. The Bank. Virtually unlimited levels to play on, 20k or less in most cases. I shot Gabriel once with a shrink ray, and he used his jetpack to fly out the window like an insect. Fifteen years ago. Still talking about it, about scenarios that to this day no game has managed to top.