It looks as though all the Android games currently available through Google Play Games for PC are free, though many of them have ads or in-app purchases. There is no option to use mobile controllers yet (hopefully there will be in future). Sadly, you can only play games with your keyboard and mouse.
Some simple one-click games don’t allow remapping, but most do. Once you start a game, you can press Shift and Tab to access the menu, where you can change the screen resolution, tweak the volume, and remap the game controls.
