Really great job. Progress was difficult, but not impossible. The snowballs of the last level were devastating. Freezing by hitting the wrong enemies was novel and fun. Well balanced. Fun. For buildings I went with blacksmith, crystal growth, and 2 mage towers. The fact that if you went too far or didn't get enough crystals, the cursor shrank back down was cool and added a balance.
I just barely made it through the last level. Which is what you want.