Hoplite

Yup, this is the #1 time waster on Android for me, a real beauty of a turn-based game :). Very simple rules apply for when you can attack enemies and when they can attack you, and as the levels progress and more enemies come into play, the game becomes even more challenging. Upgrades to the character also add to the mix of uncertainty to keep things interesting. Extra levels and upgrades are available if you purchase the full version but the game's solid even in the free version, so.... recommended!