Great game, but could use some improvements.
One of the best defense games I've played, however there is so much potential you never tapped with some of the concepts you use.
Magic: There are dozens of powerups for this that could have been implemented rather than just speed and power. In the sequel I suggest more types of spells, and perhaps powerups to add to the number cast at once.
Enemies: Good diversity, but too easy. The suicide goblins one-hit-kill was a good idea, any decent defense game needs a fast moving high damage but weak unit. More units like the standard infantry would be a nice addition as well. Perhaps ranged units that fire once they get close enough?
One other thing about the enemies, the demon lord challenges were far too easy. It would be much more fun if the demon lord spawned additional unique units.
Great game overall, but I'd like to see a sequel that is developed more.