User summary, details from Japanese Wikipedia:
The sequel to Westone's arcade game Wonder Boy. In Wonder Boy Monster Land, the player stabs with his sword instead of throwing stone axes, gains money for defeating enemies and can buy new equipment in shops for the money he has gained, effectively introducing RPG elements in a platform arcade game. In order to be able to defeat the final boss (or find his weak spot), the player also had to follow a trail of clues which included searching for hidden doors and delivering objects to various characters in the game.
The game was ported to several home systems, and saw many renamings. The Mark III port was called Super Wonder Boy Monster World and so spawned a separate Westone game series: Monster World, in which this game was the first (while also being the second Wonder Boy game). As for Wonder Boy, Sega was the publisher and would not allow the title for other than Sega systems, but Westone owned the code and for the PC Engine port, the game was renamed "Bikkuriman World", and is by far the most faithful of all ports. Tectoy, the Brazilian distributor of Monster World changed the character graphics to create the game Mônica no Castelo do Dragão (based on characters from a brazilian comic) for the Master System. Also, an unlicensed version of Monster World was also produced for the Famicon, under the title of Saiyuki World, changing the character's graphics. This conversion was produced by Jaleco.
The western version of the arcade was translated by Japanese, and was at the time a bit famous for it's 'Engrish'. Lines such as "Defeat Dragon? If so, help you! My friend, Mary lives in Baraboro. Deliver this letter, help me!" are unfortunately unavailable in the more professionally translated contemporary ports.
Details source: Wikipedia, "モンスターワールドシリーズ," available under the CC-BY-SA License.