as you progress through the levels, it feel like a natural difficulty progression. enemies in one level, then none for the next 2 levels. then enemies and obstacles for a level, then just obstacles. the increasing difficulty flow doesn't feel right. i got hung on a level, i think level 5 or 6 where the spike balls were shooting at you from the ceiling, but that was mostly my fault. the controls are nice and the graphics and background is beautiful. I never could get the character to throw the diamond forward, only drop it. I don;t t know if this was me, or the game, but I thought i would include it in comments. i like this game and love doing puzzle games in general.
If you want to add some challenge to this, make it so you can;t shoot while holding the diamond. maybe also make the spinning obstacles a varying speed, the longer your in that level, the faster they get.
4/5, 4 stars