Great game
Great game, reminded me of a Warcraft III tower defense map. However, gets a little too easy once you reach level 40. My suggestions to improve game play:
1. No reseting skills
2. Hardcore modes / Hardcore maps where you can't let any monsters pass
3. Medals should add more score
4. Glowing frame score should be higher in ~15 last levels
5. The possibility to launch multiple waves at once with one click
6. Make combining different gems more appealing. Now a pure gem is always the way to go.