Nice tower defense game, I tried the 3rd level 4 times and couldn't win it, either not enough damage to kill the bosses on the waves, or not enough HP remaining on the crystal to weather their attacks.
Made it hard not having an indication of what was coming in the next wave from the different nodes - might be something to add in future. Had to lose to realise one side needed more protection than the other during the waves :).Nice work.