Discolor Rebounder is an indie game that has a nice core mechanic. You are partly doing color matching, and partly a ball bouncer. It is the mix of two that becomes more hectic and harder than you think.
Game Play Video
The breadth of achievements is impressive. Players love to have something to shoot for, and giving them that many is really nice. Should be surfaced more in the game though. If you have that many, maybe show the next one the user might accomplish right on the home screen.
Missing Return Trigger
There is no reason for a player to return to the game once they leave. There is no energy mechanic, no daily achievement, etc.
I think the addition of some power ups, and a reason for the user to watch rewarded videos would go a long ways to resolving the monetization issues.
Players should have a reason to opt in to watching ads. Never just throw them up and make them watch. They will skip or exit your game.