In the South Pacific, Master Higgins lives peacefully wearing only a grass skirt and a cap. That is until the Evil Witch Doctor decides to capture Tina and hold her as his own. It's up to Master Higgins to gather throwing axes, fireballs and skateboards in order to aid his noble quest.
The game is a side scroller, Master Higgins moves across the screen from left to right and finds his power-ups in giant eggs. This includes a skateboard which results in a great speed enhancement - until Master Higgins gets hit and loses his power. If he is not on a skateboard a hit means instant death. Another game mechanic is starvation which gets indicated through a meter which steadily decreases. If it hits zero the hero dies and the only way to fill it up is by collecting food on the way. Bosses await him at the end of levels, all the way to the Evil Witch Doctor himself.
Although the games are indeed identical, Adventure Island is not exactly a "blatant rip-off" of Wonder Boy. The original arcade Wonder Boy game was developed by a company called Escape, who later became known as Westone. Hudson optioned the rights from Escape for a NES port of the game, but SEGA still owned the Wonder Boy title, forcing Hudson to come up with a new title for the NES version, hence Adventure Island.
In that version, Wonder Boy was replaced by Master Higgins, who was patterned after then-Hudson Soft executive and public figure Toshiyuki Takahashi (also known as Takahashi Meijin).