Just completed all the levels and what I found is that its the amount of units you use not the quality of the units you're using. You can complete every level without upgrading units or using the cannon. Upgrading is just a waste of money.
The trick is to just defend one side of fans, then when the other group get into the centre they have no one to fight with and you can take as long as you like to get rid of them. Still giving the game 5/5 great idea.
I've just completed area 3, got to the end and landed. I bought everything possible from the menu. Now that I'm at the end I get the "Reach for the stars" message but it dosn't let me click next area...
Is it possible to kill the "mighty Waizer" ?
I'm level 50, most of my stats are maxed out, I have the best wepons and armour I could get and i dont come close to killing him.