Dead Effect 2
Alright, sure, Dead Effect 2 isn't very original - and is obviously influenced by both Dead Space and Mass Effect, but it's free. A first-person shooter for your phone places you inside a zombie infested space station allowing you to unleash your frustration on the mutated horrors found inside. It sticks with the survival-horror genre recipe, cheap fear tactics, and some simple puzzles barring your way to survival. Overall, if you're a fan of shooter games and want your fix on the go, give it a shot!