A lot of applications seem to be going on sales lately, and Prey Invasion is another one that just went on sale today.  Personally, I enjoyed Prey Invasion a lot although I did find the game to be a bit short.  In my opinion, Prey seems to be one of the best first person shooters on the App Store, and the control scheme works pretty well.

Prey Invasion is an all new adventure, and the story goes that you must save your girlfriend from the aliens or monsters.  The game is controlled using directional arrows similar to that of 3D Hunting, and it is also made by the same developers of Duke Nukem 3D.  While the controls were absolutely horrible in Duke Nukem, the controls in Prey worked surprisingly well.  There are a few minor issues here and there, but the game is definitely worth the $0.99.