I'm really loving the structure of this TD:
1. Resources dependent on enemies is always a design move.
2. Inclusion of spells adds the need of active skill, instead of just knowing how to upgrade and place towers.
3.No upgrades (along with the spells) means that levels can ALWAYS have significant amount of challenge: you can't just beat them by playing level X 20 times.
Really, really smart design guys, great game!
Hmm... Nice, it's a good game for resource management, I'd like to see other works from you... have any games in production? (Or that you've thought up?)
 "Monster Arena"){kind=icon}
 "Bloom Defender"){kind=icon}
 "UPGRADE COMPLETE!"){kind=icon}
 "Super Energy Apocalypse : RECYCLED!"){kind=icon}