Nice game, love the whole don't look back thing. Unfortunately once I got upstairs the game became unplayable due to an ultra low framerate. I have a pretty decent graphics card, and other Unity games run fine, so it seems like the game could do with some more optimization. 4/5, would be 5/5 if it was optimized.
Looks like Kongregate staff wanted to front page Outbreak 2, and accidentally added this one instead. #2 can be found here:
http://www.kongregate.com/games/JaggedBladeSoft/dead-frontier-outbreak-2
Pretty good game, but really is a blatant rip off of Titan Attacks. There is no way in hell that the developer can possibly argue he wasn't heavily influenced by that game.