Been trying to play through it again on my own time to see all the postcards. Finally managed to collect them all, but forgot to read them before reaching the end, heh. I also managed to clear the puzzles in the upper path at the end, which was pretty...frustrating at times, but fun.
However, I noticed some issues with the level in one place. At the puzzle with the two platforms you have to move to go over a ledge on the left, there's also a postcard in the upper right. When trying to reach it, if I jumped while on the top platform, or any higher space really, I would get sucked into the ground above me and either pop into the house, dart left or right through the ground, or just get stuck. You may or may not already be aware of this, but it seemed important enough to mention anyway.