Not like every defense game, I like it.
I like the cooldowns over mp :) Mp's always a pain to gain, and hard to use. And the selection of spells is nice
Pros- Cooldown on spells, not MP. Allows unlimited use if you have patience. Attack is nicely done, and enemies range from easy to hard. Defend the castle, with a unit!
Cons- Only 2 spec trees for spells. Only way to regain HP is to use the spell heal (I believe..I might be wrong) Time is short before waves, but who needs time ? ;)
Improvement (opinion only)-
*Add more spec trees/spells
*More unit types
*Different difficulties or modes