If you’re wondering why this looks like a new Wonder Boy game to follow in the series after Wonder Boy/Wonder Boy in Monster Land/Wonder Boy III: The Dragon’s Trap/Wonder Boy in Monster World/Monster World IV, then you’ll not be surprised that it is in everything but name. Even the heroes of those games make appearances, sort of, in Monster Boy.
The plot is similar to that of Wonder Boy III, in that your hero, Jin, has been turned into an animal (in this case, a pig), and must progress through the Metroidvania-ish world gathering orbs. Each one of these can turn Jin into a different creature, each with different skills: The snake can crawl on certain walls and ceilings, the lion can smash through certain blocks, etc.
And it’s huge. It took me a good 20 hours or more to complete, which is much, much longer than the previous games. It was actually quite a bit easier too, especially the bosses, all of which were walkovers – even the final boss who I beat on my first attempt while barely getting hit. The platforming and some of the puzzles were more challenging, but the important thing was the whole game was a lot of fun.