I think your description of the levels is spot on!
You mention Wolf3D, and I will bring it up again because, despite it being probably even more maze-like and with a less advanced version of the engine, every level still managed to feel unique and distinct, unlike in ROTT.
If they had just done a better job of “theming” the levels (with the help of more colourful textures, and maybe more sprites for decoration) I could look past all the other flaws.
Honestly, despite some rough patches with hit-scanners and aiming and the like, the core mechanics are pretty fun and satisfying.
