How would you rate your strategy skills? Hmm, well you will need it here. You will protect some gems, so you'll need to make a plan for where to place your towers. By placing the towers right, you can defeat your enemies quickly.
It's a great time killer for me since I'm always interested in this type of game. You can remove obstacles/trees to make places for your towers and you can earn coins and spells when winning. These coins can be used to upgrade your towers to make a stronger attack.
Ads in the middle of the game can cause some players to lose interest in it. I suggest reducing the ads and focusing more on the quality of the game. One thing about its controls, I think the "Fast forward" tab won't be used at all. Also, some changes to how the tower looks when being upgraded can have a huge impact. And expanding the map too, for additional excitement.