Alien Shooter does not get cute with its title. You shoot aliens, and lots of them. With the complexity of a well-made flash game, there is really not to this title. You shoot aliens to get cash. You use that cash to buy new weapons and ammo. Sometimes the aliens are yellow, sometimes they are blue, but most of the time they are green. You can choose to set the blood color to red or green, and even password protect so the blood can't be changed back to red. I guess we all have to think of the children.
There is an isometric top down view to this game. Move around with WASD, and aim with the mouse. Most of your time is spent dancing around to avoid enemies while holding down on the left mouse button to fire. I felt the aim was not always as tight as I'd like it, but at least your character can pull off some pretty fancy footwork. I don't see a lot of options for customization in this game, so you have the choice between 9 or so different weapons, and a flashlight.
The music can pump you up sometimes, really picking up when you're fighting a large horde. The graphics are very representative of a free flash game, and yet this is not a free flash game.
If you are in the mood for a mindless shooter, I guess this can be ok if you find it on sale for very cheap. I don't think there is anything here that isn't improved upon in free games. If you are looking to spend some cash, I'd look elsewhere first.