I played through the first 3 episodes. I noticed it has glitches when you have a double-secret (two secret walls right next to each other) it shows the void when you lift one, but you cannot lift the next unless you have access to it from a side which wasn't touching the other secret wall. I think it was the second episode's secret stage where I couldn't get a bunch of the secret because I couldn't open the second secret walls.
I'm sure that makes very little sense, so let's see if google can find a map.
http://www.gamefaqs.com/pc/564603-wolfenstein-3d/faqs/40066Floor 10 is the secret level, and the green blocks are secret walls. In the instances where there are two secret walls together, the void shows up on the adjoining side when you raise the first one, and you cannot raise the second.
The only other glitch I've noticed is that the sound cuts out. You can restart the sound from the menu, though (and I'm sure through the console as well).
Other than those things, it works well.