This review contains SPOILERS! Please play the game before reading. Thanks!
I really liked this one! It's a simple puzzle, but pretty well-executed. Also love how it's a fully-realized 3d game, which is great to see. It ran beautifully on my computer. But every time I turned, things would blur--I assume motion blur was left on? It didn't really fit this game and only hindered my experience. Or maybe the blur was because of my graphics card or something, I don't know.
The pieces of the puzzle are well placed. The first things you see when you get off the elevator are the picture and the safe, and the radio gets louder as you get closer, then comes the room--wonderful way to introduce all the pieces of the puzzle that the player will need, even if they don't realize it yet.
I explored the room by first going right, traveling all the way around, and ending on the left, where the grandpa note was. Which means during my playthrough, I found a lot of things that had absolutely nothing to do with the puzzle itself--which was kind of ok, because the things I found were nice xkcd things and funny, but overall annoying because I was searching for the puzzle's solution, but found things that didn't help me get there. It would be fine if the extra stuff was maybe in a hidden place, like an easter egg, but they're framed and placed in the same areas that objects that helps the puzzle are.
Love how the radio is presented as just a simple object to switch the music (really like the music in this game, btw; all of it is great), but becomes a key piece. I'm half-upset, half-happy with the fact that typing in the radio's textbox to get the code isn't obvious? Upset because you introduce the slider like it's important, and therefore I assumed that you would need to use the slider to get the code (you can't), and happy because you present typing in a textbox with the safe, and the fact that typing in the radio's textbox isn't immediately obvious could be considered good design.
My main problem is with hearing the code for the safe. It was very hard to make out because of the static and distortion, and I got the code wrong a few times before I gave up and looked at the walkthrough. "5" sounds way to similar to "9" and that's not your fault or anything, but the static and distortion made it worse. I know that's what you intended, for the code to be hard to make out, but it was too much.
It's a good game--but it's not to the heart of the original xkcd comic, in my opinion. The point of that comic is that businesses put up the inspection sign for elevators that haven't been inspected at all--they say the certificate is on file to hide the fact that the elevator hasn't been inspected. Not that the inspection certificate is hidden secretly and not hanging in the elevator, which is how this game frames it.
I enjoyed this game. It misses the mark of what the original comic was trying to say, but I still had a good time with it. The puzzle is well designed, the 3d space is easy to navigate and well done, and the music is great. Well done.