For reasons I don’t really understand, I started playing this yesterday. On an actual Game Boy Colour as well! How exciting! I’d never played it before, but have played, and completed, the second and fourth games in the series and enjoyed them. This is more like the second, as it doesn’t have the silly race-out-the-level Wario Land 4 had, and is the better for it.
There seem to be 4 worlds, with 4 levels in each world, and 4 treasures to get in each level. So far, I’m on World 3, having got at least one treasure on each level so far. I don’t know if it’s necessary to do the lot to complete the game, but we’ll see!