i hadn't actually played Hovertank 3D - the predecessor to Catacomb 3D, and I think, the first 3D game id Software ever made - until yesterday, and here's what I have learned: it looks phenomenal. Catacomb's texture mapping was impressive, but this is one of those cases where "cutting edge" doesn't compare favorably to "state of the art," if you will.
I wish there had been more early 3D PC games with a flat shaded style like this. There were certainly a bunch of early 3D games, but they were usually more ambitious, with fully-3d-projected arbitrary polygons. This raycasting approach is faster than any of those were, and it gives a simpler, more cel-shadey tone.
The video doesn't do it justice; I recommend downloading it, or at least playing it on Archive. Suggest hitting Ctrl+F12 about 10 times to give it some more CPU cycles.