Got myself a bootleg, translated Adventure Island IV NES cart last week and completed the game today. It's a shame that this one wasn't released in English because it's a lot of fun and, in some ways, is better than the other games in the series (even though they're all fantastic games, imo). At first it seemed like it was too easy but the difficulty really picks up in level 5 to the point where the game gets a little tedious; ultimately it is satisfying to rescue all of the dinosaurs and then your wife though. Before today the only other Adventure Island game that I ever beat was New Adventure Island.
I really kind of hate the idea of people repurposing games like this but I guess not enough to resist buying this...