Yes, you're right. 90s-early 2000s/boomer shooters have different levels of "map complexity" ranging from open pseudo-flat landscapes or big rooms ala Serious Sam (afair, I haven't played one in years) with tons of enemies, to more complex mapping and enemy positioning like Q1/Q2/D3D/etc.

One can drift naturally to one or another extreme, but the more the variety the better imho. I just enjoy simpler games both in graphics and gameplay.