Critical Ops is among the newer generation of first person shooters and it’s one of the best. In this title, you’ll battle terrorists in a variety of urban-oriented levels or you can play as the terrorists if you want to. It has a strong online multiplayer community where you can play with your friends as well. It’s still a work in progress, but it seems to hit all the right marks and it’s updated frequently. If you’d like a first person shooter that’s completely free, NOVA 3: Freedom Edition is quite good as well. They're both free Android games worth checking out.