The one I'm fully addicted to right now is Kingdom Rush: Frontiers. Holee Crap is this fun.
I played and beat Kingdom Rush earlier this year when it came out on Android so slipping into KR:F was easy. I friggn love this game.
Not big on the "defence" type games because they're generally slow and too time consuming. This is neither.
Find it and give it a shot. It's tits.