Lots of little annoyances
Those annoyances really ruined the game for me.
Small game screen, even smaller targets. I get it, you gotta be precise. That's fun. What isn't fun, is getting shot six times because I can't see the dude I'm supposed to be shooting. Why can't I see him? Because he's SO TINY and almost the same color as the background. Since I'm big on constructive criticism, here's my idea: add some color to the game. Black stick figures on a dark grey background is pretty boring, and hard to shoot into. Make a little arrow pop up telling you the general direction of the enemy, so I don't have to pixel hunt.
Next up: the aiming. Oh my god, the aiming. I really don't like how the camera pans as you aim. It works in a shooter with 360 degrees of view, but with this, it's just annoying.
On the subject of the aiming, don't move the gun, rotate the gun. I mean, when I aim left, the gun moves RIGHT into the middle of the screen and blocks almost all of my view.
Bullet time! It's kinda cool, but not when it happens EVERY time I shoot while using the scope. I like the bullet animation, it looks really cool, but it gets annoying when I'm trying to shoot the birds and I miss. Satisfying when they explode, but annoying when I have to watch the slow-mo twenty times in a row. Don't get rid of it entirely, just show it less often.
All in all... I played it twice, probably won't ever play it again.