It's only a matter of cutting walls into smaller brushes [sized in sizes of power of 2, of course!] and applying a different texture. As long as the map is built on the grid, it should be easy.

Ah, the tile variety. Something I usually avoid out of typical laziness. I could try, but who knows if I'll ever make a draft that is satisfying enough to release.

I think the levels look a bit bland. Maybe you should do a bit more tile texture variety on the walls, like levels 4 and 5 of the WibiData mod, and FourthReaper's test Prolonged Exposure.

I'll think about making #1 destroyed later on in the project. First priority is to put the introduction of elements in a good order. So far, it's been up to par with the main game; portals, momentum, cubes, lasers, and bridges.

Since pt1 has the announcer and pt2 has glados, maybe make 1 destroyed and 2 clean. Then, 3 could be about gel and have cave johnson in old aperture style, and 4 could be about funnels and faith plates with wheatley style.