Visually it would be nice to see a bit more variety in everything. Would be nice if the boxes "preferred" to come from the length of the device since 16:9 devices don't leave much room for error when boxes come from the short 9 bias. More sound effects would go far to help the game-y feel.
The game is interesting in terms of gameplay but without more one-offs it can get stale and repetitive pretty quick. You do have some power-ups but I would like to see more in the way of things you shoot to spice it up a bit.
Major complaints:
-You have ads yet you do not set a 'net connection as a special requirement in permissions
-Instead of giving an option to sign in with Google Play you just auto-ask - should be an option on the menu
-You play ads DURING the gameplay on-screen (chewing up that "9" bias) and IMMEDIATELY when you are touched, before being taken to a game over screen. Pick ONE and ONLY ONE method to display ads. Having ads everywhere is annoying, especially a mix of banner ads during play and full-screen-to-the-face ads you don't see coming.
Ads should always be at the launch of the game, or after you hit PLAY, before the gameplay starts. If people are doing well and have to put the game down - how are you supposed to get impressions if they don't die to show the ad? I frequently clear running apps by swiping throughout the day that are minimized, i'm not the only one.
Regarding Google Play I remember hearing a Google conference where they advised automatic sign in (you can always cancel when prompt) saying that if people have to opt in they will be less likely to do so. That's what I did in my game, alt ought I should've had an option to disable it but never got to implement that.
The ads thing is a great solution. I have ads when you die and when you pause but you are right, if people do good and quit the app they won't see them.