I dont think it is exactly what you are looking for, but Rebuild and Rebuild 2(I reccomend the second more) are great survival games, however, they are not shooters. If you want a strategy based survival game, play Rebuild 2. You get control of a few survivors of a zombie apocalypse, and you must manage holding the fort, expanding it, maintaining food supply, and getting new survivors to replace the ones that die. I am a strategy game veteran but I still had trouble surviving on this game on the SECOND highest difficulty.The best part? They are free browser games, but they have the quality to be worth at least $20 each.