look, this is gonna sound harsh and , am sorry but... this is not good, the level design is competent (though the clipping in floors could use some work), and it has good build up but that's about it.
I get wanting to make a game about the "obey the walrus" but the reliance of the video it self felt like a crutch and the fact the last room was just the intruder face from "The Mandela Catalogue Vol. 1" just seemed lazy, and uninspired.
In another comment you mentioned getting unmotived by the end and the best advice I could give you one artist to another(granted I'm a author mostly though I have made a game before) is that you where trying to make your work something else; that thing being obey the walrus, and thus you were trying to be obey the walrus; That never turns out good. It always leaves you unmotivated at the end, trust me I've done it before plenty of times. Don't try to do what others have done, Don't be the next walrus, be the first you.
If you made a game inspired by obey the walrus and not based on it would have liberated you and more then likely inspired you as you would not be chained by the work of another and could change it as you saw fit.
So to make it short, be the first you, and nobody will be able to do you better, even if you is like something else just make sure it was you being you.
I saw you take negative critics well in some of the comments, I have the felling your young (though I might be wrong.) but if you made this in 20 hours like you've said then you are showing clear signs of raw talent, you just need refinement and some day you will be able to blow me and others away with your art and passion!