The popular Tower Defense game from Ironhide Game Studio, Kingdom Rush has gone free.
The game is hugely popular, and includes some RTS (Real Time Strategy) elements in it.
You have to fight waves of enemies, including mini bosses and bosses and prevent them from passing through your Kingdom. You have four towers at your disposal: An Archer Tower, Barracks, Mage Tower, and a Cannon Tower. You can upgrade towers to more powerful variants as the game progresses.
Completing a level with full health rewards you with a star. You can also play Iron Difficulty and Heroic Challenges on all levels to unlock two more stars for the level. You can use the stars to buy permanent skill upgrades for your towers.
Though you cannot control your units in the game, you will have help in the form of a powerful hero who is partially controllable, .i.e, you can move him/her around to take them aaway from the heat of battle, or to crush enemies in a tight corner.
Since the game has gone free to play, there is no reason not to get it. Hit the Play Store listing to download Kingom Rush for free.
Note: though the game contains in-app purchases, you can beat the game without spending a dime. If you are stuck on a level, pick a different hero and employ better strategies. You can also reassign your skill tree if needed.