Thank you for playing and for the detailed comment.
I agree with your criticism. The level design really needs more work. Most rooms have horizontal layouts where the only thing to do is go from one point to another, and summed up with the platforming challenges, the exploration ends up being exhaustive and bland. It's something that I've been concerned about for a while, trying to find ways of fixing it without remaking everything, but you've got a very objective view of the problems and it makes clear that patching up the map would not be enough. I'm not afraid of taking changes to make the game better, but it will surely drag down the development, staying longer in the first area.
I understand that the art style may not be appealing to everyone, but the game itself is meant to be niche. It's going to be a difficult game (not the same way it is now) with weird design choices and humor. The game is going to be commercial, but I don't like viewing it solely as a product. Certainly it will not sell well, but that doesn't discourage me from doing something that I have fun making and would have fun playing. It being commercial gives me a background to take the development more seriously and actually improve the game. Of course I can't be way too perfectionist, otherwise the game would never be finished, but while the development still is in the early stages, it's the best time to make changes.
Working with graphical limitations is challenging, the sprites are small so is the color palette, thus lot ends up being put to the player's interpretation, the backgrounds are the biggest example of this, and I think it is part of the fun. This particular sprite you mentioned is the one I've noticed that people were having trouble understanding, so I already planned to change it, but I can't tell what is wrong, maybe it's the color choice or the shape of the entrance, I don't have much idea.