Don't do it. Just don't. No matter how much you think you'll like this game, Alien Shooter is not a good game. All it really does is require you to hold down the left mouse button and perform contemporary piece of WASD-play to evade the countless, and I mean countless amount of green, yellow, red and blue creatures that will fill your screen at very predictable moments.
Some skill is required to keep the mouse's cursor trained on the enemy, you can't just shoot in any general direction. The map designs are not interesting at all, the weapons lack any sort of feeling to them, music gets annoying very quickly and the sound is far too soft.
This game also wins the award for the most pathetic flash light ever. Slender-man would be proud.