Awesome game! Quick and fun challenge.
Yes, it is not very realistic use of a sniper rifle (but what game is ever realistic?) - but at least head shots on everyone is hard, while body shots on everyone is easy (can even shoot two/three targets without letting sight come to rest). Realism not helped by the fact that level two and three are extremely silly set plays - ever try rushing into a room ONLY looking through the sight of a sniper gun? And then shoot targets with a sniper rifle at close range?? Oh, and the bad guys clearly purchased their machine guns at second-rate-discount-guns-r-us: so they shoot AROUND the intended target.
It is a little lousy that you need to fail each level before it is possible to complete it - the only way to snipe so many targets within the set time is to look where they all are first - why can't the shooting-timer start ON your first shot? Use a looking-timer to stop people taking too long to look around. This would probably make it feel a little bit more like a sniper game - have a quick look around, then shoot!
Maybe a good solution would be to start each level with the whole level revealed, but after a short while (very short for level 3), you can enter snipe mode - kind of make it a protagonist skill: "In the heat of battle, when the blood rushes to my head, my vision narrows, time slows, and I see the world through a scope. And I know what I must do..."
Great voice acting, and great visuals. Use of audio is excellent.