Adventure Island 4
As the final Adventure Island game that appeared on the famicom, Adventure Island 4 represents an evolution in the series. While the earlier games were straight platformers, AI4 breaks the mold by adding in some exploration and adventure elements. While still being a challenging game Adventure Island 4 is far more accessible and user friendly than the earlier games.
Check it out, it's one of our favorite games for the famicom/nes!