Dynastic Hero is good, but is definitely a disappointment compared to the original.
The color swaps and sprite changes are the most tragic things about the PC Engine Wonder Boy titles. At least Monster Lair made it through unscathed and the damage to Adventure Island is minimal.
Monster World IV is a touch easier than Wonder Boy in Monster World, and has less of an open world, but it does exude that charm and quality of late-era MD games. It was a very satisfying experience (only a
hair less so than WB in Monster World).
I've nearly beaten Adventure Island myself (only the final dungeon remains). I think it's a shame that the game has so much armor and weapons packed so close to one another - you buy one set and its obsolete maybe 10 minutes later. Spending an astronomical 9000+ gold on the crystal armor is questionable when by the time you can buy it, the Legendary Armor is available, for free, by revisiting the first dungeon.
I did have to consult a FAQ a few times in order to discover that one set of armor makes you immune to lava and that the lucky sword increases the rate of money/charmstone drops.
EDIT:
Having beaten the game, here are some general notes:
While the different forms' abilities are neat, their impact is lessened somewhat by how the game prevents easier switching between them. The mouse can only go to the jungle, the tiger through the caves, etc. If you could change them more often they would feel a bit more fleshed out other than cute sprite-swap keys. The Lizard Man is next to worthless after getting the Mouse Man.
Potions are maddeningly inconsistent. They either heal some, all, or one heart of your health. There's no way to tell. Since they don't carry over saves, you have to grind money to buy them again and again. Or still make the long trek to the only shop that sells them.
The final boss's erratic patterns are a real pain. Stunlocking you across the entire room is unfair, given his random movement patterns. The worst though is combining the boss's high difficulty with the random nature of potions. The two together have made for a very un-fun experience.
All in all, the game was good. I am trying out Monster Land / Bikkuriman now, and it's certainly different (I'm not a fan of the one-life-or-nothing set up). Adventure Island was fun, but the succeeding Monster World games are just much more enjoyable experiences.
I also picked up Mr. Heli and Metal Stoker for my fix of neo hardboiled shooting. Metal Stoker is surprising in its quality - it's a very good game.