In the sequel I'd like to see the game continue after the balloon is fixed. Level 1 could be the same as this, then lvl 2 could be a shooter. Then have lvl 3 start bc you see the monsters attacking a town, lvl 4 another balloon shooter. The final lvl could have you landing at the base of a mountain and fighting waves until the final boss shows up.
Sigh my file is gone. However that won't stop me from restarting. Plus I have a tip. If you choose the skill "long shot" when it becomes available sawmines become an extremely effective weapon. They even pass through solid objects and do far more damage than the wave cannon (forget what its called).