This was fun to play! I didn't want to quit until I snatched the gem. I agree with the other commenters that it is hard to avoid being shot. When I got through the level it felt more like I had exploited it than successfully used cover. I would stand in a way that I could shoot the enemy but for some reason they wouldn't shoot back.
Also wish the stairs worked like a ramp and I didn't have to jump.
But still, treating it like a puzzle on who to shoot first and thinking about it was fun. But that extra bullets challenge seems impossible. What's behind that button??????
Good job!