Tank VS Ufo Windows game

Just try to shoot down the Ufo's, but be careful they do get faster and you have a limited amount of ammo. 10 Ufo's, 10 shells and 3 tries to get it right. It's a simple concept that has a lot of potential. I might add some achievements or not, there's not a lot of room for expansion other then changing the graphics. I'd like to add some animated graphics and better SFX, but this will come at a later time. The end goal is to have a game that's both appealing to the eyes and entertaining enough to keep you playing.

This graphics in this game is of my own design. I'd like to have better graphics but I don't have the funds to have a pro work up the sprites. For now this will have to do, until I can improve on the graphics. So for now I'll try and work on the game play and features. Game play first and then features.

Things to add:

1. A high score list. This should be the first thing to add.
2. Achievements. I really think I should add this.
3. Multiple levels. Make the game last longer
4. Upgrades. Give the player something to work for.

I hope people like this game as much as I did writing the code.
Please do comment and let me know how I can improve it.