The best part of this game is most of the Medals actually require skill to achieve. Many games give medals far too easily.
The 'worst' part is it's not clear how to play properly at the start resulting in many players saying it's boring. There should be a basic strategy guide included. Most people quit after one try if they don't understand. I might be daft but it took me 3 full games to learn these basics:
Move all the balls into color groups until you have as close to every ball of ONE color together and then pop them. Every time you pop any balls, you get more grey Xs and more balls go to sleep.
Only use bombs to destroy the grey Xs at the BOTTOM of the screen. Any other use is a waste. Try to surround the bomb with grey Xs before popping it. Bombs have the added benefit of waking up sleeping balls.
It is vital to be able to plan 3 moves ahead when collecting colors together as often once you move a ball, you can't move it back if it was a mistake. It is normal to stare at the screen for 5 minutes without doing anything, just planning.
This is a really well made game. Not simplistic at all.