IIRC the 20th anniversary version has backgrounds entirely redrawn and pre rendered as bitmap, they're not poly anymore. The animated stuff is the original polys rendered as always, only at much higher resolution than the original 320x200. Sadly they lack detail, see notably at 2:26 in the comparison video. Also at 2:47 you can see perspective has been corrected, but the overall result is less consistent (left wall vs five spoke machine). I very much prefer the original one overall, the reduced detail and inconsistencies in art of the new one just takes away the immersion.
What I found funny about watching that is that the 2014 version is exactly how I remembered the 1991 version. Memory smoothed it all out I suppose.