Antigen is a puzzle attack game in which you control a square blue antigen whose duty is to fight off waves of germs. Each of the four types of germs has a specific shape corresponding to one of your square's four sides. You must match the correct side to each germ in order to destroy it and prevent it from reaching the far left side of the screen. If you miss too many and your host's health drops to zero, the game is over.
There are two modes of play: Story and Survival. Story mode has you taking down bad guys left and right until you reach a supersize end boss. Survival has you fighting waves of germs, each wave sending out more attackers than the one before.
I found the trackball and virtual joystick controls to be intolerably slow and unresponsive. If you have a slide-out keyboard on your Android device, I recommend using that control scheme instead. The game also supports use of a Zeemote; however I didn't have the opportunity to try it with this game.
If you can ignore the control issues, the game becomes an addictive time waster that works well on a mobile platform. Leader boards and achievements provide motivation for coming back and trying again. This free game seems to be a lite version of the game Antigen: Outbreak. After finishing the sole story-mode level here, you'll be prompted to buy Outbreak on the Android Market for $2.49.
Ultimately, Antigen fails to differentiate itself from the multitude of Android Market puzzle games. Its unresponsive controls keep it from being a great mobile gaming experience.