I wanted to say this game was good until i got to Stage 17. From that level on, it's stupidly hard to get the crystals and the Level 17 one onwards for me are impossible to get. I would say it's a greta game but i can't if the side objectives are so hard to accomplish. I hope you study changing it on a future. Also, i don't see fair that you have to adjust your own speed just to catch some crystals.
I can give it 1.5 over 5 at best. Will change my rate if i see updates on it.