Fell through the floor almost straight away and definitely did NOT take that opportunity to walk to edge of the map and jump off. Also the gun only makes a sound if a bullet hits something rather than fires a bullet which is unique. But I played it through again and collected 48 gems before finishing. The enemies are pretty easy to sneak up on and don't seem to pose any real threat.
Overall you have a decent foundation for something, but it needs some work to get fully fleshed out.