Sounds is messed up for me, meteor storm causes a constant soundscape and doesn't terminate. It appears it is based on the cursors position from the meteor storm. This is on a the Chrome browser.
The drone upgrades are a little over-powered. For most boss fights, you can just stick a drone on it's side and all bullets are deflected + your shooting at him.
So here is the best strategy I found. Look for a nice corner. First begin with about 3 missile towers. Then upgrade them. Then get to the ice and fire as quickly possible. Once you got a hotspot that a lot of stick men like to group up as of the the ice, place a bomb tower there. Now you can add more towers if you like.