A free role playing fps with about 8 hours of campaign.
Galaxy on Fire 2 is an arcade space combat & exploration game that is free to play but does include in app purchases. You can mine asteroids, explore 30+ star systems, fight aliens/pirates and upgrade your ship. The single player campaign is about 10 hours long.
Joe Dever's Lone Wolf (free edition) is a demo gamebook role playing game that is free to play but includes in app purchases that range from $5.63 - $11.99 per item, and are to buy the rest of the story.
Asphalt 8: Airborne is a free to play racing game that offers numerous in app purchases that range from $0.99 - $99.99 per item.
Stormblades is a casual action game for mobile that sees the player swiping directions on the screen in order to hit enemies with weapons in a specific pattern.
A free open world 3d RPG from Crescent Moon Games for android, where the player must attack robots, alien creatures, and travel through deserts on vehicles to get to his mission goals throughout the storyline.
Edge of Tomorrow is a single level game that is meant as a movie tie in for promotion but is still fun and more importantly free.
A 3d rpg with an "Infinity Blade" (or "Storm Blade") style of fighting monsters that spawn in the 3d world.