Man, PvZ2 in general deserved better than to be under EA's thumb. One of my issues is that the bosses are just different Zombots (which are all recycled for the final battle, by the way). If I were making this game and I designed the bosses, I'd pick some more creative options for each world.
Ancient Egypt: A zombie pharaoh who spins in a tornado of sand, tosses bones at plants and summons mummies.
Pirate Seas: A zombie pirate captain on a mini ship with a cannon on the front.
Wild West: A zombie outlaw who rides a horse and shoots plants with his revolver (occasionally summoning chickens).
Far Future: An advanced Gargantuar Prime with eye lasers and tank wheels.
Dark Ages: A necrodragon who spits fire and puts mushrooms to sleep.
Big Wave Beach: A zombie mermaid who fires at plants with a trident of lightning.
Frostbite Caves: A wooly mammoth that fires snowballs and icy wind at plants
Lost City: A giant snake that consumes plants to partially restore health and spits venom on tiles to prevent plant growing.
Neon Mixtape Tour: Disco Zombie.
Jurassic Marsh: A living fossil of a T-Rex that spawns baby T-Rexes from eggs.
Sky City: A zombie dressed as a harpy with a rocket launcher and gatling gun.
Steam Ages: A zombie with a steam-powered newspaper launcher.
Renaissance Age: A zombie's depiction of the statue "David" that shoots cement at tiles.
Modern Day: An all-powerful Zombot head that has control over time, summoning zombies from other time periods.
Only one I left out was the Kungfu World boss.