In my opinion, this is the best and most balanced of the Kid Adventure series. Levels are kept short and to the point with all levels feeling like their own thing, and difficulty steadily grows without any sudden absurdities or cheap tricks in the boss battles. Like others in the series, it follows an 8-bit graphic theme (and has broken custom music.) It's an incredibly fun fact, despite all I have to say about its flaws:
Secret exits are often very hard to find, sometimes having no hints as to their whereabouts or requiring going offscreen, but rewards such as 100% healing are worth it. There are two hidden bosses: one is in his own room and there's nothing for beating him except another exit credit, and then there's a boss inside a full level with a way of beating her even more obscure than the first Kid Adventure's final boss. The final secret exit in the hack is incredibly tiresome to get.
The points "system" where you earn titles based on your score is only spoken of in Sakito's house. What sucks is the "system" doesn't really exist - score isn't pushed to SRAM so it's lost when you reset (or beat the game,) you're not told when you earn a title, earning a title does nothing, and there's no highest score list at the end of the game. It's a shame, because one of the unlockable levels is entirely based on boosting your score.
*** EXTRA DUNGEON SPOILERS ***
In the middle of the spike ceiling is a section you can swim up and free an enemy who will sink to the bottom of the boss room. You have to disable him and throw him into the otherwise-invincible mermaid robot. If he survives, throw him out of the gap in the level. Doing so will unlock hilarious porn of the boss!