Thanks for your feedback!
To answer your question about the specific zones, the areas where you can place the door are special types of solid blocks. It was just easier to make them thin walls in the time provided during the jam.
I'm glad that you enjoyed the game. I thought that the concept was fun and interesting as well. I won't guarantee that we'll take it and make something bigger out of it, but it would be really cool if we did ;D
And, yes. Really. That's it.