Looks pretty slick. I am not a gamer, and the controls feel very backwards to me. You need to hold the mouse button to look in different directions, which makes it feel like you're dragging, but the direction you move it isn't the direction you're dragging the view. I don't think mouse capture is a good idea in the browser, and if you're aiming at museums and galleries, maybe reversing the mouse direction to make it like familiar dragging would be better.

Edit: There's a bug where if you start dragging with the mouse and let go the mouse button outside the 3D view, it acts like the button is still held down (a bit like mouse capture) which was easier but quite confusing.

It seems unusable with a touch screen on desktop.

The fact that you can fly is useful but non-obvious. I ended up down at floor level and wondering how to see the pictures on the walls.

The demo is in a /fr/ path, but is in English (Chrome offers to translate it to English, because it somehow thinks the English words are French), but then some parts of the interface like "Share your place" are in French.