Good game. Once again, I failed horribly, unless missing more than half of the disks on level three isn't bad?
I agree with others in these comments. Some disks should be like bombs or whatever in other games. They should give you a penalty for shooting them. There could also maybe be different weapons, with different fire rates or at least differing shooting animations. It would make it more of an upgrade game, while still keeping that skill element involved.
Congrats to anyone that took the time out of their day to read this entire thing. Wow to you.

Good start

It's a bit boring after a while, but it can be improved to be a really good game.
For example:
-Some more randomness in discs speeds and directions.
-Perhaps some kind of disc which cannot be shot? You know - only most of them have to be shot, but others will give you a penalty (losing lives, points, etc.).
-Sounds are a bit annoying... The best way to improve that, in my opinion, is adding unlockable, purely cosmetic weapons which change only sounds of shooting and level ending. Default (current) could be named flash gun, other unlockable could be shotgun (with its shooting sounds and reloading sound at the end of level) and silenced pistol (with simple non-distracting sounds).

Anyway - i hope you'll improve it, because it looks like you put some effort into it and you're able to make a good game from it. Good luck!

suggestions

At the moment it's pretty boring, here are my suggestions:
- add some 'drop' to the discs so they follow an arc into the distance
- it's like 'clay pigeon' shooting but not as fun because it's instant... try adding some 'flight time' to the bullets so you have to predict where it will be when the bullet reaches the target (gets harder as it gets farther away because the bullets take longer)
- add some distractions, birds & animals are ok but obvious... flying saucers or something really weird could make it more interesting
- there's no feeling of pressure... reduce the time between discs and have several flying at the same time to keep the player busy
- maybe add some bonuses that need to be clicked or hovered with the mouse to collect them

It'll still be pretty basic but that stuff would all make it more interesting.