Thank you playing!
The gravity/camera flipping can be seen as a gameplay-aberration. It is unexpected and a unwelcome change that when the gravity is inverted that looking up and down is also inverted.
As for the stuttering i sadly couldnt't fix it before the end, but tbf i only ever had two lag spikes right at the beginning shortly after loading, so i didn't think too much of it. What browser were you using and do you have hardware-acceleration turned on or off?
The grey is somewhat intentional as i wanted a creppy and steril looking environment, but you are right i should have added signs that point towards lab/office/storage/target-practice. But there also is a bug that baked lightmaps do not work with the compatibility/web renderer in Godot, so the the web version is less lit up.