I'm perfectly willing to play a mentally challenging game. There are plenty of good puzzlers out there that I've enjoyed. What I wasn't willing to do was spend half my play-time staring at the map. Many "shooters" in the '90s were as much "shooter" as "cartography simulator". Not that it was wrong that a few games included this as a major element, but too many games aped Doom and Descent's labyrinthine map-designs.
Doom did it well, and that does make a big difference.
As a different example compare early Burnout with recent Burnout games. The early games gave you tracks you had to drive on. If you failed it was really quick to try again. Later Burnout gives you a city to drive around, with tracks overlayed on it. You have to be at a certain point in the map to trigger the start of each event which sucks when you're driving back to the start to restart the event.
