Yes, there have been a million Wonder Boy games re-released on Virtual Console and other platforms, so another one doesn't seem like it would be a big deal. But Monster World IV, originally for Mega Drive/Genesis (and despite the name, the last game in the populous Wonder Boy series), never came out in North America. Monster World IV, starring a green-haired girl and her long-eared spheroid partner, is also considered the best game in the series.
According to the ESRB, Sega is finally preparing an American release of the game, on PSN and XBLA. Strangely, no Wii version is mentioned, despite the fact that Virtual Console is, like, the place for old games, and despite the fact that so many Wonder Boy games have been released on that platform -- including this one, in Japan.