Pixel gun 3d is a free app available on both android and ios. This game is purely addicting and has a campaign and multiplayer mode. You should definitely do a little of the campaign before jumping into the multiplayer mode. This game is purely a multiplayer game however and has over one million downloads.
Thats quite alot which is a clear sign that this game is pretty much awesome. Pixel gun 3d is a first person shooter with lots of guns and lots of fun. The levels are all decently designed and not too big that you will get lost. If your looking for a solid first person multiplayer shooter pixel gun 3d is a must download. Its also a free app.