It was okay

Nothing too special, better than expected though. I think you should do it properly and replace the mouse with a crosshair.

fun

better than expected

Well...

To start with, good game. In the next version I would recomennd you doing a LOT of different things. First of all, levels. And each pigeon you kill you get money instead of points, and at the end of each level, if oyu have enough money, you can upgrade a gun or buy a new one. There also shouldnt be an unlimited amount of bullets. Only the first gun you get should be unlimited.

But on the bright side good graphics/animation. Keep working!

Some ameliorations are needed

First of all, I have to say I liked this game, but there are little problem concerning to aiming thing. To kill a pidgeon you have to be aiming its head... Many time (I retry and experimented to verify this idea) when you aim for the belly or another place that is on the bird the too far away from the head, the game doesn't count it as dead.
I don't know if its because its not a deadly part, but I don't think you planned some one-shot-kill places and some other many-shot-kill places.
Apart from this aiming problem (That could be solved easily) the game is great... Perhaps you could put a little animating when a bird dies, it's a littkle absurd that when you kill a bird it disapeared that way... Makeit look more realistic.