There should be a while to tone down the quality of the game. In addition, clicking on each traffic light becomes monotonous. At least give the game hotkeys.
Zara is definitely overpowered. Every level I had her, I basically used her to solo kill the other team. Vine blocks could be sustained forever with the team heal and the AOE heal.
The boss was pretty easy. First sent a wave of 25 samurai to kill most of the front enders, and withdrew before they could revive them. Then I sent in a second wave of 15 samurai and 10 green giants. Put the samurai to kill the ranged in the back, then turned speed on. Had another wave of 7 snipers and 18 green giants in case that wave failed, heh. But gathering the giants was a pain.
Easy mode isn't a "hold your hand while I walk you across the street" easy. Difficulty is relative. It's easier than Medium, which is easier than Hard.
Save, refresh, and finish a phase when you try for the badge. See my profile if you don't believe I got the badge. And the hardest boss of the game was the 4-3 boss. The 5-3 boss simply does way less damage.
 "Pirate Defense"){kind=icon}
 "PlanetDefender"){kind=icon}
 "I Love Traffic"){kind=icon}
 "Zening"){kind=icon}
 "Crush the Castle"){kind=icon}
 "Music Catch 2"){kind=icon}
 "Celebrity Pedigree"){kind=icon}
 "The Great War of Prefectures"){kind=icon}
 "Draw-Play 3"){kind=icon}
 "Now Boarding: Episode 1"){kind=icon}
 "Oozing Forever"){kind=icon}
 "Orbital Decay"){kind=icon}
 "StarShine"){kind=icon}
 "Frontline Defense First Assault"){kind=icon}
 "The Great Siege"){kind=icon}
 "The Eternal Battle"){kind=icon}