When talking about contemporary level design, don't forget to mention one of the biggest differences between modern and old engines: the glitches are fixed! Indeed, this was
the big difference between the LPII engine (which became NeoLemmix) and old Lemmix; all the convenience features (except untimed bombers) came later.
In the Cheapo/CustLemm days, it was just taken for granted that glitches were part of the game, and glitch solutions were considered legitimate backroutes and had to be proofed against. (Cheapo, incidentally, had perfect steel long before NL, and I don't think it had sliding, but it had many glitches of its own.) It was especially frustrating because those who investigated glitches (mostly ccexplore but also Clam, geoo, tseug and others) kept them semi-secret, usually announcing challenge results using the glitches instead of explaining them.
It's weird now to look back and think how different the culture was in those days, and to remember that back then, we had no idea about how much things would change